First place to check is HERE! 😉
Go to Activity > All Hike Logs > Southern California > Ontario Peak
https://socialhiker.net/six-pack-peaks-challenge/southern-california/hike-logs/ontario-peak/
You can see hikes logged by other challengers and click to read more and see any additional photos.
Right now, the most recent hike up Ontario was on January 28th by challenger Linda, who reports that crampons, ice axe and mountaineering training is required beyond Icehouse Saddle.
https://socialhiker.net/hike_log/not-just-another-day-at-ontario-peak/
So I would wait. Often Ontario and Cucamonga hold on to snow into May. June is usually the earliest to avoid winter mountaineering there.
Ontario Peak Hike Logs