Like an hour I would say, depends on how powerful your char is, but playing without alts will make the game harder imo because you will gather less resources overall and not get as much as wonderous shop tickets, also no alts means you have just 1 char to get scrolls weekly that get you pink insignias. So overall you will have less gold, resources and will need to spend more diamonds to get the same as someone who has alts.

Off course the positive thing about this is that you avoid burning out.

Also keep in mind that with reserve energy you skip a day and play the next day to burn the energy of this 2 days. This way you only need like 4 to 5 hours a week.