There is no right time to bring ensete bananas out of dormancy. The ideal time would be at the end of April as this would give the plant a full month to grow indoors before being safe to plant out when there is no frost risk. Unfortunately most people are governed by two factors-rot and plant size.
The main reason for taking ensete bananas out of dormancy early is because they have started to rot. Should you notice this then the rot must be cut away and the plant should be potted in compost and left in bright and warm conditions so that it can out grow the rot.
The other reason for not starting them too early is that once they start growing they can very quickly out grow the height in your house!