You are talking about a roll period test. I think with google you can find a USCG roll-period test procedure.
The depth of the roll is very important. Every boat has a different roll period, flat-bottomed powerboats or large outside ballasted sailing yachts will have a short roll period, sometimes less than 2 seconds, and an ocean liner will have a roll period of over 20 seconds. Hopefully your boat will be some place in between.
A full roll is.....All the way down on one side (port or starboard), over to all the way down on the opposite side, and then back (to the starting point) to all the way down on the first side. Get three friends, a stop watch, and paper and pen. Tie the boat loosely alongside a dock. The dock lines must not restrict the rolling. You stand on the dock with stopwatch and paper. Your friends can stand with one foot on the dock and the other on the rail of your boat, and just shift their weight from one foot to the other to get her rolling. Or they can, at your call, get on and off the boat in unison to make her roll.
So they step on and off and get her her rolling, you yell stop when she's at the bottom of one roll (towards the dock is easiest to recognize). Start the watch when you yell, your friends stop jumping on and off and stand on the dock. You time 2-3 rolls and stop the watch. Do this at least 3 times, then average a single roll period.
The roll period should be close to the maximum beam of the boat in metres. This indicates adequate GM length. G is the center of gravity of the boat, M is a mythical point that's a mathematical function of the hull shape and weight (displacement). As long as M is above G your stability is positive. A rough formula for GM (feet) from roll period is
GM = (2R / T)^2
T = roll period (one complete roll)
R = 0.21-0.23 * Beam in feet
Your GM should be somewhere between 1 and 3 feet.