The reason to think in term of stops because the effects are equal. Increase of decrease exposure by 1 stop produces the same effect while increase of decrease exposure by 1 sec doesn't. If your original exposure is 1 sec and you increase 1 sec and make it 2 sec the effect is quite great. If the original exposure is 30 sec and you increase by 1 sec to 31 sec I don't think you can see any change at all. You don't have to make the steps 1 stop apart, you can make it 1/2, 1/3, 1/5 etc.. depending how closely you want them to be.
In your example increasing exposure from 32 to 64 sec has the same effect as increasing from 5 to 10 sec.