If you’re tasting ‘for serious’ - i.e., professionally, to evaluate a wine for potential purchase (either in the trade for resale, or a large quantity for aging personally), the late morning, before lunch, has always seemed to me the best time. Better than after lunch, even if you haven’t had wine at lunch. I have tasted professionally in the afternoon as well; it can work, but I’ve always felt my tasting perceptions were a bit sharper between ~10 and noon than after lunch. On our rpm Tours, we tried to make a point to taste our most serious Cabernet Sauvignon in the late morning (having a wonderful lunch at Corison was always a find combination of pleasures!)
For pure enjoyment, I suppose late afternoon or evening are both excellent times to have a glass wine. but, then, so is any time!