We have ADR’s for Cinderella’s at MK on Friday the 19th at 9:10/9:15. How much time should I allow for that/what time should I make our first LL for? We are staying off site and doing all of the single LL’s as well.
9/19 is a Halloween party day, as I suspected. Unless you are planning on hopping out of MK to another park, LLMP is unnecessary on a party day because the crowds are very low. The overwhelming majority of guests avoid MK because the park closes early at 6pm for the special ticketed events, and people think they won't get their money's worth. The park is dead all day until 4pm when party guests can enter on just a party ticket. Personally I would move that ADR to another day if at all possible, to maximize touring MK during the low crowds. I've only ever had dinner at CRT, but it's a long meal, longer than TS generally is because you have to wait for all 4 princesses to come around. I've never gotten out of there under 1.5 hours, usually it's closer to 2.
That said, if you are planning on hopping out to another park (which is a solid strategy!), I would prebook the first LL for exactly park open. The others for whatever, because they don't make a difference. We did this very successfully last year on our pre-cruise trip that was almost to the day the same time (we came down on 9/18). We booked Mad Tea Party for 8a (MK park open on party days is usually 8am, with rare exceptions), tapped in at exactly 8 after getting lucky and being able to ride Tron during Early Entry, and immediately started booking rides at HS. With only a little refreshing I booked Slinky Dog and then was able to flip my prebooked Haunted Mansion and Pirates LLs to Tower of Terror and Rock n Roller Coaster. We spent the morning riding everything in MK standby that we wanted with very low waits before we had lunch at Casey's and hopped out around noon.
In general I'm not a fan of booking TS dining on days when I'm going to be utilizing LLMP. It makes prebooking harder because the system doesn't really allow you to book LLs too close to an ADR, and it's similarly restrictive when you're there the day of. So if you can't move your ADR, and you don't plan on hopping out to another park, I would skip LLMP altogether, ride everything standby and just do Tron and Mine Train as SPs.