DIAGNOSIS You're probably not using enough liquid, or you're starting with ingredients that are too cold. This cooker needs a minimum amount of liquid to generate sufficient steam.
FIX Check (yeah, I know)—the absolute minimum liquid required is usually one cup for this size. Make sure you're hitting that. Also, if you're cooking from frozen or straight-from-the-fridge cold, it'll add a lot of time. Let things thaw or come closer to room temp first, or account for the extra warm-up in your timing.
IF THAT DIDN'T WORK Your heat source might be too low. These work best on a burner that matches the pot's base size on medium-high to high heat to come to pressure quickly. Once it's pressurized, you reduce the heat. If you start on low-medium, it'll take forever to get there.
HEADS UP The "come to pressure" time is almost never included in recipe cook times. That 10-minute recipe starts *after* the float valve pops up. So your total process is always longer.