Looking for some advice on when to harvest

Ok so i have three plants growing all going to harvest at differnet times even though they were all planted together weird situation. the one im posting now was an auto flower and started flowering while still in vegitation. so what im wondering is when do you think this will be ready it has been under a 12/12 cycle for 3 weeks now but it has been flowering for longer so here is a pretty good pic and im wondering if anyone can give me some advice

go here homie:

https://www.rollitup.org/harvesting-curing/28072-harvest-time-tutorial.html

Its hard to tell from just one picture but I'd say you've got about a month if you want to let the plant mature most of the way.

Autoflowers go straight into flowering after about 3 weeks. They take about 80 days and they are done. 18/6 is the best light regime for AF's
Thanks 80 days from dirt to scissors

i cant have it on 18 6 though because i have two other plants that are not auto flower that are in the same grow room! limited space so i have to keep them in there. fucking cfls take forever

also im looking to make the buds swell with about a month left ive heard that by dropping one of the major nutes you can achive this. anyone know that nute i think its like K or Something and another question is where can i find just straight P or something