JesterMN - If you're merely going to ride the two coasters and leave you'll need an hour, maybe two. Add in the other rides and you're at a half-day for sure. Add walking thru all the gardens, hidden nooks, etc., and you're easily at a full day [defined as "opening until 6pm"]. And of course a lot of this depends on crowds. PLEASE keep in mind that this is NOT a thrill park, but in this case it's a GOOD thing.
Bonfonte is not a park to be rushed thru. Take your time, enjoy the gardens, and ride everything you possibly can. DO NOT miss the car ride [both sides are different], the raft ride [NO rapids!], the train, and the monorail as you get unique views of the park. Don't miss the hidden Claudia's Garden.
With the Santa Cruz Beach Boardwalk only an hour away you could easily do both parks, watching the sunset and closing the night in Santa Cruz.
And please, post a trip report!