Best time to transplant from 1 gallon to 7 gallon.

I never really put to much thought into it and have always had my next crop lined up veged out for like 5 weeks under t5's so by the time i transplanted I knew I needed too. Now I'm starting from scratch, I have been vegging under 4, 600 watt hps. the stems are super fat and the plants are 1 foot tall with a decent bush to them. Is there a benefit to waiting longer to transplant? if you did it to early would it even mater? I mean considering your not worried about how much space the plants take up.

also what are your guys thoughts on dry transplant or moist transplant

Nope

"When" transplant is important is in water only soil runs.....more so for bigger plants.......
One of the not mentioned very often, styles of SS water only growing is to veg in solo's then up pot to say 2 gallon pots and at like 10 -14 days from the flip you transplant into 7 - 10 gallon pots with your "bloom" formula soil and simply water to finish.....
That's how I run my organic SS grows.
Veg in one soil formula and up pot 2 weeks from the flip into bloom formula soil. The 2 weeks allows for root growth into the new soil and the nutrition in that soil is all I need for the rest of the plants life - simply water it. No "layering or spikes or supplemental feeding"...

Doc