Love this idea!
I use my TPs more as a planning tool ahead of time rather than in the park, especially for deciding what time I should TRY to book my LLs for. Having the max range listed then optimizing/evaluating would keep the plan using the LL estimated wait, without having to finesse the actual times as often. Then when it came time to book for real I could pick a time close to the beginning of the range (assuming availability).
I believe the grace period for getting an MEP is 15 minutes. I agree this should be the default.
I think the options Len suggested are sufficient, and I would be comfortable with even fewer options. I think most people who are comfortable with >15 min will be comfortable with anything up to 60 min. Some people may be apprehensive cutting it too close to 119 minutes so more options closer to 119 would be prudent.
With all that said, the options in Len’s original proposal is probably best just for some degree of flexibility and unknowns.
Definitely a good point, though I see Len’s reasoning as well. 
Agreed - there should be no grace period for Disneyland. They are very strict for certain rides at certain times so I would not recommend using it unless it is unavoidable.
There is no “published” grace period, but reporters like Scott Gustin were told early on it was 15 minutes, which is as close to an official grace period as we will get. And based on testing, >15 minutes misses out on MEPs, and other technical stuff happens (like not being able to cancel it in MDE, I think?) that makes 15 minutes seem like a more defined grace period in the system.
What is a MEP? I think maybe I know, or used to know, but I just can’t remember!
“Multi-Experience Pass.” Aka “Anytime LL.” What you get when a ride is down during your return window.
Okay. Anytime LL! Thanks. I kept trying to make something out of that ME part. Magical Express Pass? Miniature Elf Pass? 