i was using it twice per week (1/2 tablespoon per gallon) and it seemed to work well. Or at least it didn't appear to have any adverse side affects. someone else may know otherwise, but i got some good yields and quality bud doing it that way.
Molasses can be used with every watering or every other or any combination that you like there is no magic number just like watering has no magic number it is all based on need .....best way to check for water is to stick your finger in the soil about 1.5 inches see if you can feel moisture if not water if so check again the next day....better to under water a plant than over water it .....you can always bring back an underwatered plant.... its much harder to save one you are overwatering cause of the root rot you are most likely causing by over watering.....the only danger of too much molasses is lock out ( too much salt build up in the soil ) so most seem to use it every other watering....hope this helps good luck