What are the rules for bidding for a new a/c while currently starting training on a new a/c?

I assume no restrictions to bidding so if you get awarded a new a/c ( via upgrade or upgauge), how far do they have you go into your current training before they start you on the newer aircraft?

Do they keep you in current training until your new aircraft training class starts?

Has anyone gone thru this before that could shed light on this please. Thanks.