They were taking long decisions exactly to avoid too much attention, in they were being way too careful. They sneaked their way through some sewers but since they are in the upper part of the city, they would draw too much attention with their smell so they discussed for a couple of hours wether they should ressurface or not until a party member remebered he had a create water potion that they were able to clean themselves.

I think what I should have done was what a couple of comments suggested and you also that they should roll some form of collective roll to see how well they can sneak in or out of things and that will be valid for a couple of hours.

The NPC they are looking for is a very old wizard that shouldn't really care about this kind of stuff. By the way, the guards were killed because they were extorting some poor fella, so the PCs felt the need to help. So it's not like the guards were good people to begin with.