The developers said, they would like to have a reliable combat system. Your example could also have a negative effect. For example you send an attack that should take till tomorrow when you are back but instead, your enemy and/or you close in and your fleets are back early and are getting destroyed.
I already made that suggestion a long time ago and got this answer.
Niflheim auf Asgard, das Original, egal wie sehr Consus im Forum gerne ich wäre.
- Escaria, wo Preiserhöhungen nun auch schon Bugs sind.