The short answer is more often than you think.
You can get away with a couple times a day if you are in coco and flush them well at each fertigation, at least I think you can, but twice would be the minimum. You can monitor the EC of your runoff, and if it gets more than about 300EC higher than your fertigation input, you need more watering, either more each time, or more times per day,
The issue with solos, one of them anyway, is that the tiny root space means that the plant quickly depletes the moisture, driving up the EC in the medium. Solos do best with multiple fertigations per day. When I set up my automatic solo fertigation, I fertigate six times a day.
Also, I only use coco/perlite and salt nutes in solos, I think making solos work with soil or organics would be a challenge.