Quick question ..

Left my light on 21 minutes to long. shes been in 12/12 4 weeks now and am wondering if it is going to stress her to much?

You shouldnt get any stress from anything that short term.

Not at all. Just don't do it again and get some timers.

i have 2 because i have a 250w MH and i just added 4 4ft cfl tubes to the mix and i only have 2 out of the 3 timers :/ ghetto but i want better nug