IAH Tower Controller reported using a wake turbulence rule improperly while operating in a seldom used configuration.

Narrative

The airport had just changed departure flows due to a strong northern wind and I had assumed the control position of Local West prior to a moderate departure push. The new departure flow (North Flow) is unique because of the challenges it poses for missed approaches from arriving aircraft. I was trying my best to remain aware of potential go-arounds on the arrival runway while ensuring separation between all my departure traffic. During my session I had two heavy aircraft and one B757 for which I provided separation of 3 mins or 5 miles appropriately on the parallel runway. The issue arose when I realized that I was using 3 min from departure roll instead of 3 min from departure rotation. The 3 min rule is used on parallel 33L departures because the approach end is staggered. I don't believe separation was lost; but I'm not 100% sure either. I Recommend having regulation information in the tower readily available i.e. under Plexiglas or posted throughout the work positions. Having controllers brush up on non-commonly used operations would also be helpful.