I update around 10am PST on Mondays and Fridays - Mondays are more successful in terms of views, likes and comments, while Fridays are slower and the views drop off quicker over Saturday/Sunday.
I'm still sticking to it, though, since it seems to work out just fine.
Yeah... you need to pick a specific timezone for this to apply to. I'm in CET - Central European Time, which is GMT+2. I post my stuff at 10am PST - which is 19.00 in my timezone. And there's no way for me to know which timezone my readers are in - judging from the profile info, name and time of activity for my readers, I've got people reading from all over the globe. There is no way for me to know which 3pm I should stick to.
I just go with 10am PST since Tapastic's own scheduling is pre-set to PST.