I’m planning a trip in June and am caving to my Son’s desire to see Knott’s Berry Farm, we are planning on going there on a Thursday but I wasn’t sure if I needed to get their version of a fastlane pass (cost is $100 more). If you’ve gone to Knotts on a summer weekday is it really busy? Do I need to spend the extra cash? It looks like local schools are still in session so that should help.
We went the first week of June several years ago while on a DLR trip and it varied. Their water raft ride we stood in line for 90 minutes and similar for a couple of other rides but Montezuma’s revenge we rode with zero wait 4 times in a row in the middle of the day. Pony Express was about 50 minutes, Jaguar was about an hour, etc. Overall, we waited in line more at Knott’s than DL or CA.
We were there a few years ago on a weekday in July. The lines seemed fairly long, we did have the fastlane pass so didn’t have to wait too much. I would get it if you can afford it, made the experience much better for us as we are “allergic” to waiting in line 
Early June you may be OK. And if you’re there at opening and move quickly from coaster to coater, you can do OK. Ghostrider is brutal but is so obvious waits can get long quickly. I’d start there, then Pony Exp, Coast Rider and Xcelerator. For Sierra Sidewinder and Silver Bullet you may wait 15-30. Other coasters are ordinary and optional. Don’t miss Log Ride or Mine Train. If hot, LR can get long waits that may diminish at night. Mystery Lodge and Steam Train are worthwhile, Stunt Show is decent. Krazy Kirk And the Hillbillys (formerly Billy Hill and the Hillbillys of Disneyland) play weekends but may be doing some weekdays in the Summer. There are a lot of details in ghost town so take some time to look around. And by then the new 3D ridecwill be open. If you do find you’re waiting more than you want or like to ride things repeatedly, you can always buy the fast lane in the park.