Congrats! You have a strong core!
I do something similar for my abs on an incline bench set at max height. I always do the weights in progression with sets of 10, 12 or 15. I start with 25lb plates, then 35 and then 45. If I have a lot in me, I’ll start with 35s and repeat with 45s.
I’m not sure if there is science behind it, but it seems to me that you’d be better off doing what you are doing vs holding a plank for 5 mins, for example. The thought is that you would roughly be mimicking what you do would do with weight training. [If, for example, you could to dumbbell shoulder presses of 35lbs x 25, wouldn’t you be better off increasing to 45 and doing it 8-10x?].
My suggestion: Drop the weight to 25lbs. See if you can hold the first one to 1:30. If not, stay at 25lbs for the 2nd and subsequent sets. [starting at 25, or even using just your body weight, will allow all of the muscles engaged in the plank to get warmed up]. If 1:30 is a “piece of cake”, up the weights to 35lbs. Same drill before taking on 45.
I have not researched any science behind the length of time, but I’ve done planks long enough to sense that the 1:00 - 2:00 minute range seems to work best [at least for me].
Finally, given your obvious core strength, you may want to consider adding variations that are available. One that you might find valuable is the single leg plank (alternate raising 1 leg in the air). There’s even variations of this including holding in a single leg position for longer and longer lengths of time and then hopping from one leg to the other, such that you never have both legs on the ground at the same time to rest. This drill will work different parts of your back and abs and perhaps a better use of your time than just adding weight to the same two legged drill.