Wa alaikum assalaam wa rahmatullahi wa barakatuh,
The timing of a , or breathless pause is less than the time for a stop in which we take a breath. The timing is fixed as far as the proper time to take in a , but not defined in terms of vowel counts. It can however only by correctly learned by reading and being corrected by a qualified teacher who will tell you if it is too long, too short, or just right. Of course you can listen to recordings of mastered reciters too, but to tell if your specific time is correct or not, you need to read to a qualified teacher.
Wa iyyaakum wa-l-muslimeen.
Wa alaikum assalaam wa rahmatullahi wa barakatuh.