Every WikiTreer knows the problem you're talking about. Unresponsive Profile Managers are a huge obstacle to merging.
There is a dated record when you do a merge proposal. Click to the Changes page of a profile and you should see it.
But this won't be very convenient for what you're talking about. I think we'll need to create a new system for this. Something that shows all outstanding merge proposals in your Watchlist, sorted chronologically.
I'll put this on the to-do list. No promises on when it will get done, but I think it's a good idea and others have asked for something similar.
Side-note: We're about to introduce the "match bot". This is a program that will run every night and automatically propose high-probabilty matches. It will only do a hundred or so a night, in an attempt to make sure nobody gets overloaded with merge proposals, so it won't clean things up immediately. But over time it should result in a lot more merge proposals and a much cleaner WikiTree. And make the tool we're talking about above more important.