I running a mining software at runs the CPU at 100% throughout the 3.5 hrs, which Microsoft do not like. That is actually more lenient than Google Cloud where they shut my VMs down after 0.5hrs. I think you can run it longer if you connect it via an external SSH client, like Putty or Juice SSH.
Actually it doesn't matter how many VMs you have. What matters is that each of the VM (Standard compute F4s) costs $0.4333 an hour to run and you habe $200 in free trial credits. The more VMs you create, the faster you run out of credits. But you also have more hashrate, hence potientially higher payouts in that shorter period of time. My 10 VMs per account (19 in total) lasts about 3 days of mining at around ~15hrs a day