How do I know when to switch lights?

I'm about.. a month and 2 weeks into my first grow... I think, I've kind of lost track...

The things 2 to 2 1/2 feet tall... (I've topped it) it has 3 nodes (or... crotches, not sure if I'm using the term nodes correctly) ((then the chopped top)) and the 4 other tops after that are working on their 4th node (or crotch)... How old does that sound?.. ><! I'm pretty sure I'm close to 2 months now...

I'm sure it depends on the strain, but how big or tall do these things generally get? And how do I know when to change to red light?

Using a 2' 6 bulb T5 florescent fixture (for 1 plant), It's VERY healthy looking... No sign of sex really... the main trunk and some of the branches do have some white peachfuzz, and in the crotches it just has little spikes... no balls or long hairs yet...

those spikes are called stipules and they appear on both female and male plants,..and you can switch whenever you want to..just keep in mind the plants will double or sometimes triple in size after the switch, so your own height restrictions are as tall as you can grow it..

Well, I just about an hour ago stuck 2 red bulbs in my 6 bulb fixture... should I change em all?

and holy shit... tripple?

Change them all.

some people like to have some blue in their flowering spectrum, i would switch most of them if youre not gonna switch them all, like 4 red out of 6 or something..to keep it mostly red..i just use hps.

Appreciate the info...

My fixture has 2 switches on it, one turns the outer 2 on and off, and the other the middle 4... Is there any reason for this?

And sow now that I'm on red its 12 on 12 off?

Yes 12 on and 12 off

How much room do you have to offer for your flowering stage? basically count on double your size. so if your plants are 2' now count on em being 4' when flowering. You can veg as long as you want just depends on your room size and what you can handle. Good luck bro.