I averaged it out over a month last year and on average from full power to 3,000 AGL and back down to the runway was 12 minutes. I can do it faster but we are under a Class Bravo shelf extension now so I will cut the power back a little bit on the climb out after reaching 1000 AGL so that we slow the climb down and I am able to get the gliders outside the shelf. Pattern tows can be done in less than 6 minutes. So when figuring out my times for the day I will take the patterns tows and count them two for one and then add them to the 3000 footers. Then I multiply that number by .2 for entry into logbook. We dont do many tows over 3000 anymore because of the Class Bravo above us now because it would require some manuevering to avoid controlled airspace.