Also, I've been looking at a target block window of ~96 hours (still a bit short for my tastes) for the hard fork block target.
I was going to say at least 3 days from release but 4 is probably better. Need enough time in case exchanges/pools run into some unforseen issue with compiling, or something else rears it's ugly head when it's in actual use and thus requires canceling the hard fork ahead of time. So yeah, I have no problem with at least 4 days and wouldn't complain if it was even 5 or 6.