I just failed a 455lb dead lift, tried to down scale to a 405lb which I've been able to pull 5 of previously and failed at that too. How long do I rest prior to reattempting a previous max (405lb at 5 reps) and then reattempt the 455 level lift? Is it a week? or more? or less?
If you're following a regular weightlifting plan, you're likely weightlifting every other day. As a result, you should simply resume on your next workout day.
Since your most successful lift was 435 lbs, you can start with 440 or 445 lbs. This way, the increment isn't too large to throw your body into a panic or lose your self-confidence.
Just ease yourself into it and you should be fine.
Overtraining (or whatever name is suitable here) is a gradual process. If you abuse your body for an extended period of time (too much lifting and/or too little rest), you need an extended period of time to recover. As far as I have seen, mostly is used something like 1-4 weeks.
You should also consider what you will do in this time - easy deadlifting could be fine or doing something completely different (less destructive) may be better in various cases. The time and level of deload should really depend on how you get in the failing mode.
Kind note: IMHO if you are not experienced professional, I would guess you should never fail - at any cost. Training near your limit produces improvement, testing the limit produces failure.
In case of in-training rest between re-attempts, please see the following chart taken from (https://www.strongfirst.com/patience-of-strength/ - not the original source):
(minutes on the X-axis, strength in % in Y-axis - note that 13-20 minutes it is possible to produce higher output - for this given case - it could be different for DL 1 rep max)