I went to go exercise the lance last week. When I requested my taxi clearance, there were no planes in the pattern, so of course by the time i got to the hold short life, a seneca, an arrow, and an archer, all from the flight school, came in to do pattern work. My question is, I was cleared for takeoff right after the wheels of the seneca touched down. They were cleared for a touch & go, and were right at the 1000' markers; i was at the approach end. The archer was just turning base. I thought there had to be at 3000'of separation on a runway. Because the seneca is faster than me, I guess the tower controller could assume that by the time i got on the runway, they would have the seperation? I wasn't comfortable starting my roll so close behind the seneca, so I lined up and waited until they rotated. I still got out in plenty of time ahead of the archer, but they seneca flew a huge pattern and I had to extend my upwind or i would've been turning inside them. I don't have any complaint with the controller; he did a great job managing 4 aircraft in the pattern with a bit of a spread of performance, and the arrow was doing power off 180's so that added another wrinkle. I was just curious about the requirements for takeoff seperation. @Timbeck2 is there any or is it strictly performance based? I was concerned about having enough room to realize & stop if the seneca had a rejected takeoff.