For example, I have the beer at 73F for its diacetyl rest. After FG is achieved, would it be okay to bottle the DIPA at this temp and leave it at room temp (68F) without harming the flavor?
I reckon that should be just fine. That's how most homebrewed bottle conditioned beers are handled, isn't it?
Allegedly, the little bit of O2 introduced in this process is supposed to be gulped up by the yeast when it replicates during the carbonation process.
But... I truly doubt all of it gets consumed and whatever remains around will cause a negative impact on your beer, especially diminishing that great hop sensation.
Now if you decide to cold crash (with or without gelatin) to clarify a cloudy beer, you may as well bottle it when it's still icy cold. Then let the bottles come to room temps naturally and start their carbonation process, which should take around 2-3 weeks, perhaps a bit longer since it's a DIPA.
Just make 100% sure the beer is really done, and the bottles are well cleaned and sanitized, so you don't bottle infections and potential bombs. I think people bottle a few 12-16 oz plastic soda bottles on the side to verify progress of carbonation and all is A-OK, FG wise.
I wish others would chime in, to corroborate that this method is actually sound.
Solutions to limit O2 exposure?
Maybe flushing the bottles with CO2 right
before filling, or at least flushing the headspace of each bottle
after filling, right before capping, may help. If possible, both. I don't know if
O2-absorbing caps actually deliver on their promise. Seems almost too good to be true, maybe just advertising hype. I've never used them, can't really tell.
Alternatively, you could keg the batch, (force) carbonate, then fill the bottles from there using a counter-pressure bottle filler (BierMuncher's method of a #2 rubber stopper over the filling tube) or, if you have one or can borrow one, a beergun.
That way you may be able to keep oxygen exposure to a true bare minimum, or even totally eliminate, by doing a (closed) transfer from fermenter into a 100% liquid pre-purged keg. Flush the bottles with a shot of CO2, fill, and cap on foam immediately, or flush the headspaces right before capping. An extra set of hands surely comes in handy for this.
Instead of using a bottling bucket, you could use a keg for that, instead. It allows you to transfer and work under CO2 as I described above, while bottling.