Without using whatever method you've used before, not really.
What you can do to make it easier, since it seems you're only using ULX logs and not Garry's Mod's own log function, add "log 1" to the server.cfg and it should log everything that has happened in a folder called "logs" in your server directory. This should make it less messy, because instead of logging what happens per day (correct me if I'm wrong about that) through ULX, it logs per map and creates a new file every mapchange. Although, in the end you might have a bunch of files to look through, but it should be easier to find the right time if you sort them by "last modified".