Anybody know where I can find the distance/ time standard for last man up?

There isn't. It's intended to be a sprint. Time and distance varies widely by size of the formation, pace of the formation, and fitness of participants.

Here's something we are going to in the SOF community:
Distance is a human construct. The body doesn't understand distance. We invented it.
What the body understands is intensity vs time. Planning PT around this method allows ass soldiers of all ability levels to achieve the same intensity and effectiveness in workout in the same amount of time, eliminating the slow runs with bored runners, and fast runs with epic fallouts.
So something like "you are going to run 10% faster than your APFT pace for 3 minutes, then take a 3 minute walk" (repeat 6 times). Everyone does the same time and intensity, but the "distance traveled" will be different based on their own ability. You could even do "12 min out, 12 min back based on their APFT pace (% faster) and everyone, in theory should return at the same time.
It's much more effective and includes everyone equally than the other "PT" the Army has.