This is discussed on DMT nexus quite a bit. It is not recommended, but it has not killed someone. Never the less people have had negative effects and I have read of an ER visit after using changa on MDMA. Safe bet would be to wait at least 24 hours. The important thing is you wait until the MDMA stops releasing extra serration into your synapse while your MAO are inhibited so that the extra serration is not broken down and causes reception overload essentially.