Music duration

[René Micout]

Hello !
Actually my problem is making music with Rev (hi Beat !) on QuickTime  
Synthesizer via PlayCommand Agent X (Shakobox : hi ! Jacqueline).
I have two solution to "do" duration (schematically):
1. First solution :
A. Start sound
B. Wait x millisec
C. Stop sound
2. Second solution :
A. Start sound
B. Send "Stop sound" in x millisec
With the first solution the sequences (and duration of and between  
sounds) of sounds work very well but if I have a second sequence the  
sound of this second sequence stop (and wait...) with the "wait"  
command of the first sequence.
With the second solution the independance of sequences is right (no  
waiting...) but the sequence is not right because sounds overlap and  
do not really follow...
Someone have a third solution to satisfy both requirements ?
Excuse me for my english...
René from Paris