it is easier to dissolve the molasses in hot water as then the water can dissolve more of the sugars and some of the longer polymer lines are already cracked down by the heat (needs energy to crack the links) or otherwise you give the input mechanically by stirring as mad to get it fully dissolved
you could use it with every feeding but it can plug up the soil a bit and slow root grow in the extreme which then would lower your yield, so to be on the safe side you feed em molasses as you feed fertilizer: every third feeding. if you feel confident that your grow can take more then that you surely use more then that.