Hay nako, yan talaga ang siyang frustrating mama, that 10:30pm wake-up window is so tricky! A few of us mums went through similar with our toddlers, and honestly, it could be anything from sleep regression, discomfort, or even his internal clock getting confused, kaya I'd really suggest bringing it up with your pedia para ma-check kung may underlying issue like reflux or ear infection na hindi obvious. In the meantime, try keeping his daytime super consistent (same meal times, same play time, same outdoor exposure) kasi sometimes toddlers' night sleep improves when their day routine is rock solid, at maybe check if the room is too hot or if there's any light or noise waking him at that time, totoo talaga na 10:30pm is such a specific window, parang may something triggering siya then. Hang in there, totoo yan ang exhausting talaga!