quiet you…
We’re working on customizing the search for whatever number of people you have. There’s a parameter to pass in MDE’s API for it.
This all applies to pre-planning, not in-park:
60-90 seconds is more than reasonable given the calculations involved and… the TIME SAVED waiting on lines at WDW. 
I have always optimized first, then added FP+, then re-optimized after adding FP+, then possibly changed FP+ and added more attractions based on the result, then tweaked/evaluated/tweaked/evaluated/repeat. Clearly/intuitively, knowing what the machine (and this human) is trying to accomplish, this is the way to get the most out of this most wonderful tool.
Sometimes I take its FP+ recommendations, sometimes not, so many variables a machine couldn’t possibly know about. Each day/objective has its own challenges, as you well know.
I do think it’ll be important to have some kind of message that says, “Please be patient. Expected wait time for optimization w/FP+ 60-90 seconds. Your call is important to us; please don’t hang up.”
I also think that any time a computer is going to make a real/actual FP+ or any other real decision on one’s behalf, the default setting should be “OFF”, and the user should have to turn it ON to activate such a feature.
The idea of “fixing/unchangeable” FP+'s is a very good one.
In fact, it could be applied to any/all steps in a plan, not unlike meals/breaks.
Occasionally, I’ve done just that: make a step into a “meal” to “fix” it in place.
Again, it’s a marvelous tool. There are workarounds for almost anything. 
As for In-park optimization… I have less opinions about that, as I tend to stick with what I planned… though I confess that might be to my own detriment. Flexibility can be bliss or a curse.
If I think of other things, I’ll add to this.
I’m sorry I haven’t been around much for about a month. After the most recent trip, I had ODed on all things WDW. I hope to jump back in soon & write a long-delayed “trip report” with some silly insights, but some “life” stuff has taken priority recently. Thanks for tagging me to get my attention on this. Very much looking forward to seeing what TP becomes as you continue to “slay the ever-changing WDW landscape/dragon.”
BTW, unless I’m unlucky or mistaken, it seems to me that the average wait time on the WDW web site to do anything, whether it’s loading an ordinary page, making an ADR, booking a FP+, or checking availability or scheduling on just about any kind of attraction/entertainment is probably 2-5 minutes… even worse on mobile. Just sayin’
We think we can parallelize some of those read-only requests. Also, the API calls may be faster than whatever Disney’s doing for screen rendering. We’ll see.
Cool. Looking forward to it. Thanks!
Like that a lot! Otherwise, I’d be pretty nervous
This is my big “wish for” as well. It would be great to have an option to “lock” a FPP into the plan, in other words.
Awesome work around. Thx for the tip