Wondrous Item, uncommon
As a Magic action, you can open or close this bottle.
Opening the bottle causes thick smoke to billow out, forming a cloud that fills a 60-foot Emanation originating from the bottle. The area within the smoke is Heavily Obscured.
Each minute the bottle remains open, the size of the Emanation increases by 10 feet until it reaches its maximum size of 120 feet.
Closing the bottle causes the cloud to become fixed in place until it disperses after 10 minutes. A strong wind (such as that created by the Gust of Wind spell) disperses the cloud after 1 minute.
Blind fighting / Skulker and this item is really good early game combo.
Can you open/close the bottle repeatedly to get the smoke to spread faster than it spreads on its own?
If you're opening and closing it in one spot I'd rule it as no, given that it said it only fills a 60ft area when opened. However you can be creative and move around opening and closing it making more 60ft areas of smoke, since it said the cloud remains fixed and disperses after 10 minutes and doesn't say that creating a new cloud removes the previous one.