What I want to do is start playing a track and at a certain point in the song I want it to loop until I'm ready and then it carries on until the end of the track. Is that possible on the HD 2500?

Yep!

...and it gets better than that, it two ways ...

1) The DN-HD2500 offers 2 seamless loops per side. So, for example, you could have a tunes intro looped to aid with mixing or voice-over time not exiting into seamlessly playing back the rest of the track, AND have a second seamless loop say looping the 4th chorus back to the 1st chorus to make a great track last longer, again until you press exit to alow the track to carry on with the remainder of the tune

2) The DN-HD2500 allows you to store your seamless loop points, and cue points etc in something called -Memo Points-, when you've got them just how you want them (you can edit them frame by frame) - next time you select a track which has a memo point stored for it, a memo indicator appears on the display and you are asked whether you'd like to re-load the stored cue point, seamless loops etc.

You can store upto 50,000 memo points per hard drive.