I feel like most people think their workouts have to be a minimum of one hour in length in order for them to be considered "good," and that's the furthest thing from the truth. The length of a workout is not directly correlated with how effective or good the workout is, especially when it comes to ab workouts — in fact, a five-minute ab workout can totally be effective, as long as you're doing a variety of exercises that target different core muscles and you have good form.
You may not know this, but even if you aren't doing specific ab-strengthening exercises like planks and bear holds, you're more than likely still strengthening your core. For example, exercises like deadlifts and glute bridges target muscles in your lower body, but they also work your abs! You don't need to spend 30-plus minutes training your core, and I'd actually recommend against it. Instead, you could be spending time focusing on exercises that target muscle groups in your legs and arms, helping improve your overall strength and allowing you to move better, while simultaneously targeting your core.
It's OK to add a quick ab circuit to the end of your workout for core-specific strength training. And if you do this, I advise making sure you mix up the exercises to prevent overtraining one part of your core and undertraining another part. For example, you don't just want to do a bunch of forearm plank variations, as that will primarily work your anterior core (your rectus abdominis muscles, aka your six-pack muscles, and your transverse abdominis muscles, which are deep core muscles), which stabilizes your lumbar spine (lower spine) and pelvis.
Instead, you can and should mix it up and also incorporate exercises that work your lateral core, like side planks, to prevent too much side flexion and prevent you from falling over to the side; exercises that work your posterior core, like Bird Dog and deadlifts, to avoid excessive rounding of the lumbar spine; and rotational exercises, like Russian twists and chops, which help prevent too much lumbar spine rotation.
If you're worried about the length of your ab workout, don't be. As long as you're working all the muscles in your core and modifying or progressing the intensity of each exercise or workout contingent upon your needs and fitness level, you'll be fine!