Hi there I am Dm and I'm having trouble coming up with how to run a particular travel session / Encounter. 

Background Information

My players are delivering a large package via pony and cart to a remote hamlet in an area heavily laced with fey magic. There is a road that takes a tenday, or they could off road it (difficult but not impossible with the cart) and it takes about 4-5 so long as they don't get lost (very possible as the fey magic around here is tricky). An unknown NPC has instructed the surrounding Gnolls in the area to look out for these travelers and destroy them, in particular the package. One boon the players have (tho they have not been told) is that the pony is especially attuned to the dangers around them, it has a detect good and evil aura up to 30ft, and if the players follow its lead they gain advantage on survival checks to not become lost. 

What I want

I want the Gnolls to be actively hunting the party down while they travel to the hamlet, perhaps forcing them off road in an effort to make it there faster. I  want there to be a pursuit level threat much like OotA but more immediate? It felt like the drow purist was suppose to be over several tendays. I would love to use Skill challenges to have the players try to navigate around the Gnolls and the rolling craig infested hills around them (think Scotland moors). I want them to be constantly afraid that they gnolls will catch up. I would love for the players to figure out organically that the pony is more than just a regular pony.  There is also a particular battle field/graveyard I'd like the players to stumble across if they leave the roads.

What I don't want

I don't want it to be a one stop fight and continue on our journey. I don't want it to be one short skill challenge for the entire journey. I don't want the gnolls to completely overwhelm the players (at least not till the very end of their journey and then I can have some militia from the hamlet come to help bring them to safety) I also don't think I should have them rp out each day as that might become tedious and boring as they are likely to do the same things each day - perception and survival, rinse and repeat.  

So Does anyone have any ideas or tips on how I may achieve my goals? Any brainstorming help would be appreciated. 

As a player, I wouldn't even consider trying to take a cart into the woods to avoid pursuit. It would be terribly slow going and open us to all sorts of ambush from the gnolls. The slow speed means the party wouldn't be able to get away to shake pursuit and regroup. It would also leave an obvious trail and make it easy to follow. And given the woods are full of fey magic, again, as a player I would avoid if all possible.

Also, as a note, Detect Evil and Good won't detect the gnolls. That spell really should be called 'Detect Outsiders'

I would propose the following:

the players set out, and get ambushed by the gnolls fairly quickly (one or two days), hopefully forcing them to flee up or down the road. The gnolls are lazy and know they can't get anywhere too fast, so they don't rush to hard to catch up initially. Because of the fey magic, the road dead ends after a day of travel. Make sure to describe a sense of weirdness to the players while they had been traveling so they get the hint that this isn't Kansas anymore. To find their way through the road in the fey area, they make Survival or Arcana checks, and if they notice the pony's behavior, they get advantage. It takes some number of successes (5?) to find their way out. Gnoll pursuit starts at 4, each failure increases pursuit level by 1. Throw in some random fey encounters to slow them down if needed. On one of the days, they go past your battlefield encounter.

Ok I can see where you're coming from with that. The danger needs to outweigh the benefits of staying on the road if I want them to even consider leaving it. 

Would your opinon change if I had the Gnolls concentrating on the roads and setting up ambushes along the way. The idea behind that is the gnolls would know the safest way through would be the roads so they should attack there. 

I could also have the pony gentling trying to lead them off road. Rping him being obedient but also looking off off road, pawing at the ground, trying to move in that direction but stopping when the player tugs on the lead rope, and looking mildly frustrated.

On the note of detect good or evil, thanks for the heads up, i agree they should change the name. I always considered gnolls to have a bit of fiend in them given their origin so ill probably flavor it so it still works. But it is good to know so i can clarify and dont confuse my players.

Ok i like that a lot with making the roads affected by the fey magic. I can work with that.

Would you suggest i have them make those survival or arcana checks each day or 5 successes total for the whole trip?

I would have them make a single group check each day. Adjust the DC to be higher or increase the number of group successes to make it take longer. With a group check, everyone makes a roll and half the group needs to succeed for them to pass. Each person would individually choose either Survival or Arcana to roll that day against the target DC. You could also throw in other skills sometimes, like Athletics because an obstacle needs cleared, or Medicine / Nature to deal with a weird fey fungal bloom spore cloud.