I want to use this for a second home. We only have the wi-fi turned on 6 months of the year, but we need the system all year. Can we set up a predetermined watering schedule and the turn off the wi-fi and let that schedule run?
A fixed schedule will indeed run indefinitely with no network connection. However, you won’t get rain skip / freeze skip / wind skip, though you can use a hardwired rain sensor to suppress watering when it rains.
If you’re not too far from neighbors, you might get one to let you mooch off their Wi-Fi.
Or, assuming you have cellular coverage there, consider a data-only SIM in an old mobile phone configured as a hotspot. You may find this useful for several things other than Rachio. For example, open a networked lock to let a contractor in, or monitor and control your HVAC system.
Podgroup offers an ‘unlimited’ SIM on T-Mobile, throttled to 64 kbps for $2.75/mo. including all taxes and fees.
Telnyx has SIMs for $2/mo. + $0.01 per megabyte, though I have not checked how much data Rachio consumes. This is full-speed, so it could be useful for viewing a security camera.
Various MVNOs offer low-end data-only SIMs, e.g. Tello $5/mo. for 500 megabytes.