You can start carbing with the CO2 tank now, and at any temperature, as long as you refer to the chart in the stickies to set your pressure.
So you have to:
* choose a carbonation level
* know the temperature of you beer
* check a chart like this one: http://www.kegerators.com/carbonation-table.php (for higher temperature, google will help you find a different chart)
* set you pressure accordingly. In 1 week carbonation will be OK, in 3 weeks it will be perfect.
If you keg will sit at room temperature anyway, you can use priming sugar: boil 2.5oz of corn sugar in a quart of water, add this to your keg, seal the keg by hitting it with 30psi, unplug the CO2, and wait 3 weeks, like you would wait for a bottle.