This terrific warmup allows student choice: goo.gl/ZTtH79 (30 second video version - runs a little better than Slides version). Let students choose which exercise to do for each period of time. (There is an uncover and a beep upon each slide change to students will visually and auditorily know when the next exercise is up.)
Slides version: goo.gl/qaAE3n. One link will move forward every 30 seconds and the second every 60 seconds.
You can, also, manually move to the next slide if you think it's time by simply clicking anywhere on the slide, however this will stop the automatic timer. To reset to the beginning for the next class, it's easiest just to close the window and click the link on the slide to begin.