Blood testing is monthly for the first month or so, and then 3 monthly until they are stable, then 6 monthly. I really wouldnt delay the meds though, from talking to a friend with thyroid problems, it really does make you feel yucky, and either I have a very odd cat, or it is very easy to be missed until the thyroid levels are quite high, as my vet wouldnt have even tested Sam last week without my insistence (and my feeling was off such minor things like paws feeling warm, not sleeping in one place for too long - not the typical hyper-t symptoms like excessive eating - his weight loss was only picked up on due to his monthly weigh ins). He is a lot calmer and more willing to sit on my knee for ages after just one week of meds. He has taken 6 months to go from being bang on the end of normal to being classed as hyper-t (his levels have gone up by 20)