Long cycle lengths, first time user question

Hi, trying the Ovulation Testing for the first time and I want to make sure that I start testing on the right day. My cycle lengths for the last 7 months have been: 28,32,33,37,40,30,36; going off the suggestion of the 'use the shortest cycle over the last 6', that would mean I use 30 day cycle, and that means I start testing on day 10. Is this correct? I just started this current cycle 2 days ago (so I am on day 3), and don't want to get my window wrong. Thanks!