Hi, ChangingiCloudEmail,
You cannot set the duration of a still clip to less than 0.1 sec in iMovie 10.
However, after you set your photo clips to 0.1 duration, you can share that as a File to your desk top. It will share as an Mp4 movie file. Then import the movie file into a newly created iMovie project. Because it is now a movie file you can use the speed adjustment feature to speed it up. The easiest way is to control- click on the movie clip and, in the drop down menu that appears, select Show Speed Editor. That will reveal a speed adjustment handle in the upper right hand corner of the clip. You can then put your cursor on the handle and, while pressing down, drag the handle to the left to speed up the clip or to the right to slow down the clip. It makes it easier to make speed adjustments if you first expand out your timeline with the little slider located above and to the right of the timeline, next to the Settings button.
An alternate way is to click on the speed adjustment icon in the tool bar at the upper right of your screen (the one that looks like a clock face) and you will be able to make custom speed adjustments from there.
-- Rich