I had a 50’s prime time ADR for 4:40pm, which is OK but ideally I wanted to try to push it out a bit, maybe to 5:15ish. Set a res finder… got a notification for a 4:50, so I took it, then immediately re-started the search (which I have set to find a table for 5pm).
About 5 minutes later, I got a notification that a res was found… at 4:40pm! Imagine that! 
I guess I’ll wait a while for someone to snatch up the 4:40 that I dropped before I restart the search, lol!
I’m going through the same thing! I want a 10:30 Garden Grill breakfast and I have a 10:00 and there’s a 10:05 available they keep texting me! Lol I am glad I’m not alone!
What about setting the search time for 5:45 pm in res finder?
It seems to cast a pretty broad net. I’m not sure there is a way to pin it down more. I got past the 4:40 one (someone must have grabbed it), and had it searching again set for 5:00, and just not a notice for a table at 6pm. At this point I’m OK with the 4:50 so I’ll just stick with that if I can’t get anything for 5:00-5:15, but I don’t really want anything later than 5:30. 
Quote from res finder page:
Time of Day: If you choose a specific time of day (rather than a meal), we will search for a reservation within 60 minutes of that time.
This is why I thought you could avoid the 4:40 pm from popping up by putting in a time of 5:45 pm (which would search 4:45 pm - 6:45 pm). Of course, later times than you want may pop up, but if it’s for a restaurant this is usually full during the 5 pm - 7 pm range, you might have better luck in avoiding undesired times coming up in your search.