I use it in VST mode inserted in the FX bin.
On my old lap top I had to do what Kalle said...load only part of the song..... work on it and then bounce it then hit the next section and so on. BUT, on my DAW that I built 3 years ago, I'm able to load entire song tracks and have no problem. I have even had 3 tracks with melodyne on them running.
It all depends on your computer, the memory, and how many other things are in the project and running in real time.
The only nit I have with melodyne and start times is that melodyne plays to it's own clock. So if I start playback, and then click on the time line to instantly rewind to a specific point..... X1 makes the jump and keeps playing from that point which I just clicked..... but melodyne keeps going like nothing happened and they are out of sync totally.
If I stop playback, and then click a new start point on the time line, melodyne starts from there just like it needs to and plays perfectly in sync.
I can also listen to a track and have one note that needs repair...that maybe I missed somehow. All I need to do is set my start time a measure before that note..... place melodyne in capture mode.....hit play to let melodyne capture the few bars of music..... and hit stop at any point after the note. I can edit that note.... bounce the result to the track and life is good.
But you are correct.... you can not select the start time from inside melodyne's GUI. It must be done in X1's start time on the time line.
To me that is not a big problem.