I had a small + departing full length. Then a small approached an intersection and I said hold for wake turbulence. So I depart a different small full length directly after the small + (6000ft/airborne). Then I thought the preceding aircraft was a small, so the small at the intersection could roll directly after; there's no WT for 2 smalls. My interpretation of the 7110.65 3-9-7 states this is possible. Even if the intersection aircraft taxied to the intersection after the second small departs then calls ready, would you have to keep track of the three minutes from two departures ago or do you go by the preceding aircraft (previous departure)? Thoughts?