When will I get my iPhone back from Apple?

I shipped my iPhone for a repair on Sunday for repair because it was having unexpected restarts. It's stuck on diagnosing product status.

Step 1Request
February 17, 2016: Product received by service center
Shipped via UPS with tracking number
Step 2Service
February 17, 2016: Diagnosing product
Step 3Return
Serviced product return pending

Added (1). I have a iPhone 6s Plus.

Could be anytime this week or early next week

Should contact them through an email (or whatever). Not like your iPhone is the only thing to deal with.