I second the issue that pictures stop changing after a set timer. Didn't measure it but 2 min sounds accurate. Maybe vocalize your disappointment through Esdeath if her slave isn't in good shape to meet her expectations ;).
Wanted to bring up a wholly different issue.
I had a freeze today after Esdeath explains todays goal. No big deal but it kept getting the same freeze even after reloading couple of times. So I opened the tease in a private window and tried the reset function for the first time. I checked my cookies in the non private window which showed me my stats (didn't save them, so thankfully I could look up them this way).
I noticed the bpm to be fishy and doing some additional tests I noticed every time I reloaded the tease the bpm decreased.
Imho the tease should only progress if reach a certain point is reached (ruin, punishment). If you fail maybe the bpm shouldn't decrease at all but that's up to you, the teasemaster.
Edit: Minor detail I forgot to mention. I think there should be slightly more prep time after additional conditions (e.g. kneeling). Maybe add a additional dialogue line like "take out your dick now" to signal its about to start. Unless Esdeath wants us to ruin it by rubbing it over the pants