If you come early to your minyan in a minyan factory for shachrit and you're able to hear the entire torah reading from beginning to end, do you have to stick around for YOUR minyan's torah reading the second time around?
IE:
Your Shachris starts at 8:00 am.
You arrive at 7:45 am.
The previous minyan just took out the torah scroll.
Can you pay attention to the previous minyan's torah reading and leave right after shemonah esrei or do you have to listen to your own and stay until the end of the shachrit of your own minyan?
But if you catch an earlier kriat haTorah, you cannot say ashrei/aleinu with them and be yotzei for the next minyan. What you could do theoretically is to say ashrei/aleinu on your own in your minyan and leave during kriat haTorah. But CYLOR because this cannot be routine practice
– mbloch Dec 21 '15 at 17:47