for the first question:
maybe something like:
import time
training_start_time = time.time()
#train your 100 epochs
print('Training finished, took {:.2f}s'.format(time.time() - training_start_time))

for the second question:
It kinda depends. If you want to get the best accuracy you can take it from a specific epoch. You can also calculate averages. Even the way my calculate accuracy can differ. You can, for example, take top1 accuracy or top5 accuracy. It’s really up to you