How long does it take for an initial charge with MBP?
Power it off. The first 80% should charge in 2 hours. The last 20% should charge in the second 2 hours. 

If the battery was deeply discharged I would repeat that test once you get the battery full and then drained. 

Contact support either way to have them check the full charge capacity and review your powered down charge timings. 

That protects you and gives Apple the data it needs if you feel it wasn’t a great battery. In the past, Apple would ship closer to full. Now with changed airline regulations and changed chemistry in the batteries, they ship mostly empty. I wouldn’t worry once you get your two tests in and contact support. 

Everything you say seems perfectly normal, but for sure shut it down and do a controlled test - now is when you want to be sure it’s fully operational.