Oh, I get it now. I thought your allies were outside (normal time), then there was a slow-nut (unoccupied, acting as a "force-field"), then the inside (normal time) containing you and your enemies, in which case you're vulnerable to them for the entire time the ambush is set up. In which case, the above problems apply.
But you're not. You're saying your allies are outside (normal time), then your enemy is in the slow-nut section (slow-time, vulnerable), then you're in the inside (normal time), thus your enemy can't attack you while the ambush is set up.
Yes, that would work fine, and is a good idea, but would require careful positioning and timing (pardon the pun) to pull off. It's a good idea, though, and could be very powerful when it works.