There used to be the functionality to add together different recordings but it hasn't really gotten much testing, so it was eventually removed.
The best thing you can probably do is copying the same timeline between different replays as explained in this video https://www.youtube.com/watch?v=e51Fxoyd7Sc (beware that it's quite old, so some advice in there might no longer be accurate).
Using the pause/resume functionality will still record everything (that's fundamental to how the mod works) but then cut away as much as possible from the parts where you paused and squash anything which it cannot cut into one point in time.
The only thing you can do against sudden change of ingame time, is installing some third-party mod (idk of any but I'd be surprised if none exist) which allows the client to have a different (fixed) time than the server.
To jump during rendering just put two time keyframes right next to each other. Should be quite obvious when once you understand how time keyframes work, so you might want to read up on that.