To my best experience you need to run yoyo at least for 2 weeks until the RAC becomes stable. Iam runnig yoyo@home on the same device 24/7 since 2 weeks and the RAC is still rising. At the moment i prepare a comparison between 4 different devices and platforms (Arm on linux , Android, x86) and the RAC is still not stable. For project with short turn around time per project the RAC is stable much faster. Some work packeges in yoyo take more than 2 days - so you may throw away a lot of CPU time when canceling the project on day 5.
RE: Is android mining worth it? - The Gridcoin test