I think there should be somewhat of a time elapse before players can rank up either using: /rankup, /buy 13, or /buy promotion...Since sometimes players use: /give and it doesn't really serve as a true identification that the player earned it. I know pay should not be given(as i would suggest) to ops. But this is just an addition for server owners who would like to have their players still use /pay command.
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Ideal Suggestion:
The time elapse should probably be set to 28 minutes to default. I chose this number since when a default lava server starts up the round like "14 minutes left to lava flood." Server Owners should be allowed to change this number though.
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How to Implement:
Spoiler: