Unconditional Generation Training Time

[BenoitWang]

Hi @sharvil @Andrechang @JCBrouwer thanks for this implementation.

My issue is about the training time for unconditional generation. It takes me about 5 hours/ epoch on 1 * RTX8000 and most of the time is spent on loss.backward(), with the unconditional setting in #5, I wonder:

1. Is this common?
2. Any suggestions for acceleration please?
3. From how many epochs that you start to have good-quality generations?

Thanks in advance.