Is there a window for the minimal time to ETS and am I supposed to participate in scheduled field training within that window.

Start your backwards planning process:
How many days of Terminal Leave are you taking +
5 days for ACAP +
14 days for clearing post +
Medical Appointments +
Finance and HRC appointments =
How long you will need for Transition

Tally those days up and see how close they fall to the RETURN from your unit's NTC rotation. If you should be starting your transition process before you return, then you should talk to your chain of command (TL, SL, PSG, 1SG) *** Do NOT jump anyone in the chain! You're screwing yourself if you do...***
Additionally, have you gotten a replacement for your position yet? Have you conducted a 'Battle Handover' with said replacement? If not, your CoC might have you going in order to get the replacement up to speed.
Good luck!

You're best off asking your FLL since you're a short timer. I would anticipate going to the field unless you've got some approved leave prior to you ETSing.