I'm running a campaign with my players in which they're commonly roaming around settlements searching for clues to solve mysteries. I generally like to keep track of time that has passed - each of my players is equipped with a calendar to measure days passed. But when it comes to measuring time in, say, hours, I tend to get confused a lot. This usually ends up with the group having to stop for a while to figure out where exactly they are in the day.

I was wondering if anyone has any tips for tracking time in towns, villages, and cities. I considered an "action" type approach (e.g. each player has 6 actions every day, 3 every night) but I found that to be a bit convoluted after a while. I'm wondering how to measure how long the tavern scene lasted, how long it took them to find the blacksmith, how long they spent buying food at the marketplace, and so on. 

i think it is not the best answer but you can just make it up  and say it took you 1 houer to get to the marketplace and all the buying and bartering took you 2 houers so it is 1400 
you can just say your party what time it is or how long it took 

Unless the campaign demands it for some reason, just make it up. Shopping in a marketplace can take minutes or hours depending on what the PCs are looking for and whether any vendor has it. Hanging out at a tavern can also take up as little or as much time as you want. Think about the last time you went with your friends to just hang out. How much time did it take? Generally a sit down meal with a server will take about an hour, and a nice meal up to three. 

Again, just make it up. "You've spent a couple hours going down the various aisles of vendors looking for the hoozit. Lots of whatzits to buy, but no hoozits. Just when you are about to give up, you see a young lady packing up her two-wheeled wagon. Peeking out from under a blanket you spy what looks to be a blue hoozit. What do you do?"

"The air in the tavern is filled with the smells of roasted meat and light song from a traveling minstrel. The meal was great, and filling. A fine way to pass the evening. Just as you place down coins to pay, a man bursts through the doors, looks around manically, and points at you. He stumbles a few steps in your direction, then collapses. You see a dagger protruding from his back. What do you?"

I'm definitely a proponent of "making it up" - whatever's reasonable, and that can change as you get more practice and experience in the skill.

If people are splitting up and doing different things at the same time, I think you can write down "Name ##" for who is doing something for however many hours. (I only have 3 players, so it's pretty easy to keep track of without needing to write it down) Then I'll ask the others what they're doing during that time and determine how much they can get done in that amount of time.

Then repeat that process to keep everyone progressing at the same relative time.

If the players are also sticklers for time, then have them help by writing down what they want to do, you telling them how long it takes to do that and the player writes down that number. Then you can check in to see who has time to do stuff and who's done everything they could do in a day?

Just spitballing here. >.>

First, I would suggest a tool that I've become very fond of: Fantasy Calendar. This tool has the ability to be customized in any way you feel and can help you track the calendar days easily.

For tracking time of day, I'd suggest reading Angry GM's advice. This bit of a read really helped me figure out a way to play with things and even though it deals with long distance travel, it also touches on daily events too. 

In the end, time is entirely up to you. You choose to say that it took 10 minutes or 45 minutes to search a room. You choose to say it took 3 hours to craft a potion, or 3 weeks. You could say it's 20 minutes to walk across town, or you could say it took 2 hours. You are in charge of giving those time increments, the only thing you'd really need is a notebook to keep track of how much time has passed.

Good advice above. Another handy tip is to mark time on a map. Often you'll have a distance key, but for ease of working out, you can always work out how long it takes to travel the same distance as the key and add that to your map. Now when someone wants to travel an inch on the map, you already have it written down that an inch equals 30mins walking/20 mins running or whatever depending on the scale. That can help with travelling around towns, particularly large ones like Waterdeep or Neverwinter.

Something else you can do is ASK THE PLAYERS. They amount of time they spend somewhere is tied to what they can find/hear/discover etc. So if they're in a marketplace and they're looking for the aforementioned hoozit, they can make an investigation roll for each 30 mins they spend searching. Or whatever. So depending on how much they want the hoozit and how lucky they are, they could find it straight away or it might take 2 hours. But it becomes the players choice. Same with searching dungeons, trying to find info in a tavern and so on. Just remember to factor in impacts of time. You want to run across town instead of walking? The chances of you getting stopped by the town guard will increase. You want to spend half an hour thoroughly searching a dungeon after you've killed all the nasties? Random encounter possibilities are going to stack up. You can even go as far as asking if they want to put away their weapons to be able to search easier. Have you ever tried rummaging through a cupboard or in some blankets while holding a Bow? Not too convenient. So maybe they get advantage if they put them away. Of course then if something comes along, that's going to put them at a disadvantage when they have to defend themselves.

I made a round-counter, which can easily be modified to count hours.  In Word (or my fav.-libre Writer), I just created a 1-row table of boxes with the numbers 1-10...about one inch down the page, i took a copy of that table, pasted it a couple lines down, and flipped the picture vertically...then printed the whole page out, and cut off the top 3-ish inches of the page so that just my work is left.  So you're left with ~3 inches of paper, with nothing but 2 rows of numbers, one upside down, with white-space between the two rows.

I then fold the paper in half long-ways in the middle of the white space between the two rows of numbers, and hang it over my DM screen...so I can see one row of numbers, and the players can see the other side....and both sides appear right-side-up.  I then put a paperclip over the current time. It holds the paper on the DM screen, marks the time for both sides, doesn't hide any info on the screen, and I just slide the paperclip as time progresses.  Since one picture is flipped, the paperclip is covering the same number on each side...its just that one side counts right-to-left, and the other left-to-right.

For hours, just go 1-24 and you can make the numbers as small as you'd like, just depends on the size of your paperclip as you don't want it circling 2 numbers.

Total investment is one paperclip and one piece of paper.

I'd like to suggest also that the general adventuring day has 2 short Rests of and hour long each, and the long rest of 8 hours. That cuts about 10 hours of time. But also a good tip is using a 6 sided dice to represent 10 minutes intervals for each reaction. Once it hits 6 one hour has passed.