When you reset time you keep any major items, warp points and learned songs. The best way to tackle a dungeon is to reset and slow down time and then take on the dungeon from the very beginning of that cycle.You generally get access to a dungeon by completing a quest and learning a song. You just need to do this quest once and when you reset time you can just warp to the dungeon and play the song.
As I understand it getting 2 dudes to record a thing almost every day takes a tole on the schedueling they can't afford. Recording a metal gear scanlon whennever Dan and Drew are available seems more manageable.
Endurance Runs were never recorded every single day. They did a few long recording sessions and then cut it into separate parts. It's really apparent in the P4 ER as Vinny keeps making jokes about it.