I feel like 早上 is much earlier than 上午, but I don't know the exact hour boundary between these two. I usually use 早上 for the time when just get up, and 上午 for the time that is closer to lunch time.

早上9点前 上午9-11点 实际应用无具体界限

早上分为清晨和早晨， 清晨：4：00- 6：30 早晨：6：30- 8: 00 上午一般是指 ：8 ：00- 12 ：00 早上到晚上，一般是指早上7：00- 晚上 19：00

You really need to get Chinese input! 上午： morning 下午： afternoon

actually there's no differences