"Concurrent Duty" flying commercially while in the military

I am new to the site and the industry. I am actually writing a paper about pilots who fly commercially but are in the reserves. Can anyone here give me some insights into this? I want to know, practically speaking, how the process works. Do you just schedule yourself to only fly when you don’t have military obligations? Is that possible? Are the airlines friendly to this practice? (I understand that legally an employer must give you that time off and allow you to come back to work but I am looking more for what happens in reality)
Thanks for any info you can give me!