Wio Terminal low power mode

I powering the Wio Terminal with battery/solar and want to turn either turn it off or set it as low power for 8-12 hours a day.

I am using Adafruit’s SleepyDog Library (using the sleep() function) but it only seems to sleep for a maximum of 16 seconds.

If I want to keep it in sleep mode would I use the RTC to check the time and put it to sleep every time it wakes if it is between certain hours? or;
Are there other options? (are there simple 5v timers available?)