how often can i check my plants before...

you can check as often as you want (but less often gives you more change to observe )
the only thing to avoid to do this is interrupting the dark periods, making big temp flux, etc...
when you go in there, breathing on/around them you even give them some CO2 to work with
so that's that i'd say

 

sounds almost like you're worried they can't stand your face or something

 

Just out of curiosity, I've heard that same thing before, but is something like the C02 you're giving to the plants even noticeable in the end result if you're around them much? I have a setup of 5 plants in my room

 

One of my good friends grows and we always try to stay out/away from the grow area. The less you open the door, the less chance a mold or bacteria can get onto the plants.

 

Opening the door often, brings in fresh CO2 or at least be bringing in air from an adjoining room via a fan. You should have an in fan and an exhaust fan. They say singing to your plants help, I think it is just the Carbon Dioxide you are breathing on them that makes them react. Look at them as often as you can, but let em rest during the dark periods. No exceptions. Even a small amount of light during the dark period can throw them back into veg and mess with the genetics.

 

My ladies are a week away from harvest and I always check them in the morning and in the evening (after and before 'night'). I check the PH and PPM, room temp, nutrient temp and log the numbers on a sheet along with any notes of things I've done (added PH up/down, RO water, ...).

Good Luck!