That never happened with me. I always pretty much start the real battle right after the demo fight is over and my Rowdy dies or the target had no fighters to fight with.

The only time I was not able to attack someone because of a shield, was yesterday when I tried to attack @hiddenblade with 1 Rowdy to say hi lol, but she has a shield because she just started playing.

If there was a 4-hour break, the whole plan could turn useless as the target would have plenty time to either invest their resources or use them to make more troops.