photoshop changes my gif speed?

hi. i've been using photoshop cs5 for about 6 months now, and ive noticed it changes my gif speed a lot. heres how i make my animated gifs:

i load dicom files, create animation frames, crop 268px by 150px, make frames from layers, flatten frames into layers and sharpen each layer, and then, heres where the trouble comes. i set my speed to 0.05 per frame, but it goes so much slower than that. i convert to timeline, and if i click the button to go into frame animation again, it says that my frames are set to 0.07? i hope this makes sense, because i tried to change it to 0.04 a lot of times too, but that gets changed to 0.03. this is really really frustrating, because i make gifs for sites like tumblr and its annoying that i can never get the speed i want.

please help?