Hi TB
Watering confusion eh!

I've used biobizz lightmix before and watered a few plants so i'll do my best to help.
So you got a little un about a week old. The tap root wont have sunk to the bottom of that pot by now, and you don't want to be putting litres of water through at this stage.
So at this stage, you don't want to water too much. 500ml over the week will be ample (if not too much) - At this stage, I'll be giving my girls half a cup every three days or so.
What to do!?
Measure up 500ml of water and 0.5 ml of grow nutes (guess you got biobizz grow). Give it a bloody good shake/mix. Give the little un half (if the soil in th pot is not saturated and wet.) of the mix.
Throw the other half away - It's just good practice not to have pre mixed nutes laying around (others may say different)
Pick up your pot - feel the weight.
Go back tommorow and pick up the pot - If its "polystyrene" light (it shouldnt be) it needs water. If not, go back tommorow.
give it another week of the 500 ml thing.
When you have a few sets of true leaves - mix up an entire litre with nutes (following whatever guide your following (hopefully an auto guide ^_^)) and then water it slowly until it starts running out of the bottom.
you dont want your pot to sit in this - the reason you want "run off" is to push any salt buildup through. If you let the pot sit in the water it will "wick" the water back up (doh!!) - the solution is to raise your pots on some stilts (use your imagination, i used small squares of wood)
If you didn't get run off - mix up another batch and continue watering until you do.
About 10% run off will be good. (100 - 200mls)
Umm. yeah. After than pick up your pots every day. When they're light light, it's time for watering.
When they get old they may need watering every 1 or 2 days. Only the weight of the pot will tell you,
If you over water, the leaves will look heavy and droop.
If you underwater, the leaves will look limp and droop.
If you're leaves are drooping and the pot is heavy - don't water. Vice versa if the leaves hae drooped and the pot is light - she needs watering.
Hope this clears up the water issue.
(don't forget to PH the water after adding nutes Soil wants 6.2-6.4ph)
All the best
Blue ^_^