By mid cycle I mean randomly through the cycle on different days. With Vetsulin, it usually peaks in action between +3 and +6 so concentrating on that period will likely get you the info you need which is how low the dose is taking BG. One day do a +3 and the next a +4 , then a +5. If you find Conner is doing most of his dropping early in the cycle, then that is the time you should check him going forward....if he's later you, can test a bit later. It's all about figuring out what your cat's pattern is and then testing accordingly. I'd periodically grab a test after +6 as Vetsulin has a second "hit" around +7 or thereabouts but it's much smaller and not always noticeable. At night, if you can get a +3 or at least one test before bed to make sure BG is not dropping too fast or too much, it gives you the opportunity to intervene if you need to and gives you some data about what's happening at night. A lot of cats go lower at night so it's a good idea to periodically try to get a little later night time test but obviously we all need our sleep so getting the early test helps fill in the big picture of how kitty is doing.
Some folks use Polysporin with pain relief on their kitty's ears. Perhaps his ears are getting sore. Are you poking in the sweet spot rather than the vein? Are you applying a bit of pressure to the poke spot after testing to prevent bruising?