Allow me to explain how the energy system works at the beginning of a round.

As long as you join within the first couple of days. No one else will have an energy advantage over you.

The later you join, the more energy you start with.

However your starting energy has a cap of 300, so if you wait too long then it will hit this cap and you will have lost out on energy that could have been spent if you had joined sooner.

The moral of this story is although you should sign up at the start, the start lasts about 2 days.

Which means that now, would be a perfect time to join.