Like someone else already mentioned, spidey's webs are formulated to break down over time. Iirc, he has changed the formula to change how long that is, for special circumstances, but it's usually described as "a couple of hours".

I don't recall any canon description of a hard limit to the timing, up or down, either. So it could be adjustable down to near instant to practically forever.

However, there is also web solvent mentioned a few times over the years, though no description of it beyond that comes to memory.

Now, afaik, the formula isn't even really described as to exactly what it is. I vaguely recall one of the older issues mentioning it being like silk, and a much later generic "polymer" being used, but nothing was elaborated on in any of the issues I've read that I recall. I have read everything up to maybe ten years ago or so at least once. That's when I discovered certain sites and programs that allow one access to digital copies for free, and spidey was the first character I binged like that, him being the first superhero I ever cared about (enough to have worn out a dozen sets of spidey underroos before 2nd grade).

Anyway, can you imagine how annoying it would be if it didn't dissolve on its own? There's been a few scenes where people bitch about the webbing as it is lol. A bunch of grumpy New Yorkers having to wait for city services to come along and deweb a sidewalk? Holy crap ::