If your filter and gravel have you 40 cycled as long as you only add the convict for now there is no concern as your adding no more bio load and have more water volume. You can add a new fish right away. It's the only way to start colonizing more bacteria for your tank as they need the fish waste. Get a test kit and add your first tank mate. Do water changes as needed until your filter catches up.
Sent from my SM-N900W8 using MonsterAquariaNetwork App
Sent from my SM-N900W8 using MonsterAquariaNetwork App