[Threshold]

(PlayerInfo[playerid][pMuteTime] / 60000) = Milliseconds / 60000 = Minutes.

1 seconds = 1000 Milliseconds.
1 minute = 60 seconds = 60 x 1000 milliseconds = 60000 milliseconds.

So replace PlayerInfo[playerid][pMuteTime], with (PlayerInfo[playerid][pMuteTime] / 60000)

EDIT: Or (PlayerInfo[playerid][pMuteTime] / 1000) if you want it in seconds.