Is setting a time to shut down the computer – to avoid staying up late and to sleep early and wake up for Dhuhr prayer in congregation – considered a vow of obedience or a permissible vow?

The expression "I promised myself" is not a vow (nadhr), because it lacks two conditions: it is not among the binding formulas, and what was promised is not an act of worship (qurbah). Therefore, nothing is binding upon the questioner.