Also from my personal experience, I use Sweet and Molasses approximately "whenever I remember to" at the rate of 10-15mL/gal Sweet and 1 glob molasses in the watering jug (holds a couple gals) and shaken well before app. Super extra awesome visual results can be attained by adding some SnowStorm to your flowering nutes, and even at a fairly low dose the 'look' of the crystals is improved.
The nice thing about carb synth products like sweet and topmax is that they are reasonably gentle to the plants and within reason, exact scheduling and measurement isn't going to make or break your grow.