There should of been a chart that comes with your regulator...
http://www.randmsupply.com/images/link/REG-1instructions.pdf
Thats the link to the regulator I use, but if you scroll down you will see the chart I speak of. Without knowing the height of your tent, I'm gonna guess its 6 feet tall... now lets do some math... 7 x7 x 6 = 294 cubic feet... with 294 cubic feet, if you set your regulator at .5 then it would reach around 1500ppm in 30-35min.
If it were me, I'd set it at a constant .5 and let it rock out... don't forget to set a timer, plants don't need CO2 with the lights OFF, so don't waste it!
Hope this helps.