With the recent release of Google Cloud Scheduler to beta, we’ve published a step-by-step tutorial on using Cloud Scheduler to schedule start/stop of GCE VM instances. Please take a look!
In parallel, we’re also looking into ways to make scheduling VM operations even easier.Steven Edouard commented
There's a 3rd party product called VMPower.io which does this by simply scheduling time slots on a weekly calendar. It also supports utilization based shutdown so your VMs can turn off after low cpu/memory/disk utilization.