Perfect Boss Fight Times
These timings start the instant the prior level was completed, and end the moment you spawn for the next level. That means they include the cutscene and wait after boss death (excepting Diablo, since you are awarded the win the instant Diablo dies).
Bot2K
For Bot2k, you should almost always be able to have a perfect fight by picking up all the energies as they spawn while keeping the laser's energy under 325. Occasionally you can get really unlucky and have to wait, but that has only happened to me once.
Bot2K perfect time: 3:27
Bot2K perfect time: 3:27
Odin
There is some randomness in the Odin fight as to where he walks while in the water, which will determine how fast he is killed. Additionally, if you can manage to kill him in 1 flood rather than 2, that will save you nearly 30 seconds - since it takes the flood 28 seconds to rise and start zapping - assuming you don't tank too much lightning (however, I have yet to encounter a group of people who are actually willing to try to kill him in one flood, so I don't know the exact number).
Odin double flood perfect time: ~3:20
Odin single flood perfect time: ~2:50
Odin double flood perfect time: ~3:20
Odin single flood perfect time: ~2:50
Diablo
The cutscene + countdown for Diablo takes 27 seconds, after which Diablo will cast 1 ability every 10 seconds. After 4 abilities, he will summon chaser drones, which means after 40 seconds chasers will spawn. It takes chasers 17 seconds to explode after their spawn. Accounting for slight variablity in when Diablo starts casting abilities (he casts them every multiple of 10 seconds game time, rather than every 10 seconds after the fight starts, which means you could waste up to 9.99 seconds), this puts a perfect Diablo fight around 1:30.
Diablo perfect time: ~1:30
Diablo perfect time: ~1:30
Perfect total boss fight time: ~7:50 or ~8:20 (single and double flood Odin, respectively)