Sounds like you have an old Hunter controller thats a PITA to program. I suggest you dump it and move to a wifi controller. I installed a Rachio. Takes about 30mins to install and trust me you will love it. App on you phone will allow you to turn on and off zones to check. Connects to local weather stations that knows when its raining etc. Had a Rachio is California for many years and now have one here in TV.

Amazon.com

I am wondering if the problem may be related to water pressure???
Have you noticed a substantial change in water pressure throughout the day?

I choose to run my system on manual mode only, 30 minutes per zone. A deep soaking much less often.

Water pressure will not turn on a valve, only an electric signal will trigger a valve. Up north where you have to winterize your sprinkler system, I had to turn off the water so I can turn on 1 zone at a time to blow it out, no pressure or the lack of pressure did not have any impact to valve turning on.
If I was going to run a system in manual mode, then you need a wifi smart controller so you can do this from inside your house or anywhere in the world

Just purchase a new Wi-Fi Rainbird timer … start screwing around with the old timer and you may smoke your solenoids… Your old Timer took a Dump… always make sure you have a Great ground connection… this is lightning country …

Factory Reset the controller and start again...

Hunter Pro-C:

https://www.hunterindustries.com/sit...OM_ProC_EM.pdf
Pro-C Basic Programming | Hunter Industries

Sometimes the controller programming freaks out.

Closing out this post with a big thank you to Ron, the Hunter expert. It was an electrical problem. He diagnosed it almost instantly. (I will try to explain it here as best I can) About 2 years ago, we had someone add a zone for some backyard plantings. When the zone was added, the wire used to connect the valves was a thin wire. The other wiring was thick wiring. Over time the thin wire lost contact; the reason it would work later in the day is that when the temperature warmed sufficiently, the warmth created expansion and then the wire would get contact. Ron wrapped the thin wire around the thick wire for constant contact.

Also a big thank you to all the other great minds on this thread and TOTV overall. This is the place where smart people, creative thinkers, and true experts come together to solve problems.