Usual advice on ALL thyroid tests, (home one or on NHSu) is to do early in morning, ideally before 9am. No food or drink beforehand (other than water) If you are taking Levo, then don't take it in 24 hours before (take straight after). This way your tests are always consistent, and it will show highest TSH, and as this is mainly all the medics decide dose on, best idea is to keep result as high as possible
My very senior endo, was most insistent I should not take Levo in 24 hours before test. (Perhaps because they recognise there is an over reliance on TSH and also want to keep it as high as poss?)
I normally take at bedtime, but just delay until after early morning blood test. Still take next dose at bedtime later the same day.
TSH has been shown to have a fairly wide diurnal variation, and is highest very early in morning.