I'd mention it so at least your T knows you realize it. Maybe say "thank you for seeing me so promptly" or something too? I did that once; my T went away for 6 weeks or more and I forgot what time we normally met! I didn't think to call and ask (since she was away, my brain was thinking she was away until the moment I saw her again :-) so I took off work and just showed up and was several hours too early. But she showed up early too, guess she wanted to get some other work done LOL but saw I was in bad shape so just saw me anyway.