[user5994461]

You typically want exactly 0 or 1 instances for testing instances. I don't recall autoscaling groups able to do that.

[skywhopper]

This is entirely possible. Scheduled actions can make this happen on a schedule (simply schedule desired-capacity=1 when you want it on and desired-capacity=0 when you want it off). Or you can simply run a command to do it on demand.

[rabidrat]

I have an autoscaling group that goes from 0 to 1 every day for some batch processing. It took a bit of finagling but it's definitely possible.