Here's what I all fit in on Friday, April 16 - a little delayed here but crowds are probably very similar.
Walked 17.8 miles in one day - only park day in WDW in 2021 after my AP expired - hopefully going to DL in June, so wasn't too worried about getting on a lot of rides in MK since I can do them in DL
Got to MK turn styles at 7:10am for a 8am opening, went right to 7DMT, it was not running yet, I was pretty close to the front of the line (a little past pooh) I think if I had arrived more than 10 minutes later, it would have been smarter to do other rides first and do 7DMT at the very end of the night (but I wasn't staying in MK all day either, so I definitely wanted to get it done)
The line started moving at 7:35, I got on at 7:46a
7:53a - I wanted to do peter pan since I assumed it would be a walk on and it was right there, but it wasn't running yet, small world was running, opted against doing that.
Hoofed it to frontierland, 8am and big thunder was a walk on, did it twice in a row - splash mountain still hadn't started running yet while I was doing BT, it was running by the time I got off and said 5 minute wait time on the app lol that was not accurate, app changed to 50 minutes soon, but I only waited 20 minutes after getting in line for it at 8:20a
9a - 2p in MK I literally just stalked all the characters because my past trips I had been to busy on rides to see the train station characters and I really wanted to see all of the different groups. Then I saw all the cavalcades. I walked around and took photos and had sleep hollow & citrus swirl in between some of the longer gaps between cavalcades.
in depth report of MK characters I made here: https://www.disboards.com/threads/character-sighting-tips-frequencies.3834767/
Left a cast compliment at guest relations (I'm sure this is very much appreciated if you have time and have a special experience with a cast member and was very easy to do at guest relations. I'm sure the guest relations CMs also enjoy hearing positive stories instead of being yelled at most of the day haha, the CM at the door seemed to have a sigh of relief when she asked why I was there and I said a cast compliment)
Got in the MK to epcot bus line at 2:08 and was at the epcot pylons at 2:34. Went around and took photos and got the orange bird shoulder plush at mouse gears (no where else seemed to have him!) Saw princess cavalcade and mickey, and really just took a million more photos of all the topiaries until 5:45. I knew I would do rides after the sunlight was gone! The crowds weren't bad at epcot, like I was able to get most topiary photos without waiting or people around, except for the darn france pavilion! We could really use the extra space around the rat ride!
Skylined over to HS and got there at 6:10, I was taking photos near MMRR in a minnie mouse inspired outfit and a CM saw me and asked if I wanted to ride, and I was like yes I am definitely going to later! And they were like no, you can ride now through the fast pass line

Posted wait was 25, I was intrigued to see how long posted wait was VS actual wait, but not intrigued enough to decline the nice magical moment!
Mickey and Minnie came by right when I got off MMRR just sweetening up the evening experience, and then I wanted to ride tower at 6:45 and was assuming the 50 minute posted wait time would be inaccurate, but i got tired trying to find the end of the line when it started to go into the fantasmic area and was worried it would end up being pretty close to posted wait time.
7pm - one hour until HS closed, Placed a mobile order for woodys for 730 pickup, ran to toy story land and did TSM (posted 15 min wait, it was a walk on), 715p - Alien was 15 minute posted, I didn't get on until 7:27, wasn't expecting to actually wait around 15 minutes!
Rookie move to not push "I'm here prepare my order" on mobile order earlier, I should have pushed it before I went to the bathroom, not after while I was just standing in the waiting area for mobile orders with everyone else looking dumb and sad and hungry. Very quickly ate (brought the tots to go in my purse whoops) and got in line for Slinky at 7:46 - posted wait was 45 minutes but the line didnt even extend past the actual entrance where the sign and times are listed! Got on at 8:06
Took my TIME getting to the front of the park (my feet HURT, went to get some band aids on the way out) - the skyliner line looked LONG, and I didnt want to have to wait in another long line to transfer, so I wish I could tell you how long the wait was but.. I took an uber back to epcot. I also knew I wanted to go right to spaceship earth and didnt want to walk from france, so it was worth the $23 uber for my feet! Finding an uber or lyft was a PAIN, they kept telling me there were no cars, and was I SURE I wanted to take a car? Not the only time it was hard to find a ride at peak hours, so plan ahead for that possibility.
Got in line for spaceship earth at 9:03, got on at 9:12 (20 minute posted wait)
9:40 - walked on nemo, wow i forgot how long that line was though just of walking time, my poor feet and my dumb self for not having better shoes

9:50 - figment was a walk on.
10:15 - frozen said 20 minute wait, got in line where the troll topiary is, got on at 10:25. Do not love the plexiglass at all, but i have no room to complain when I only waited 10 minutes for frozen!
10:45 - How were my feet still functioning now - I am not sure - Soarin said posted 30 minute wait, I got on like in my seat at 11p.
A+ way to round out the longest day in the history of my feet.
Meant for this to be a posted wait times vs actual wait time post, but got carried away

Hope this helps someone though! Do toy story rides and epcot rides super late at night! (No idea about test track tips though besides jumping in line for that one at 10:55p if possible i guess!)