Training twice per day to accelerate progress?

I have been lifting weights for about one year and only in the past 2-3 months have really gotten serious and began eating & lifting for the purpose of muscle growth.

I am 5'11 (180cm) and 154lb (70kg) and eating around 2100 calories per day. My current training is:
back/bi's
shoulders/tri's
legs/core
And I just cycle this 6 days a week.

I am not working currently so am left with a ton of free time to go to the gym and focus on my goals. I want to accelerate my muscle growth as much as I can and really utilise my free time to its full potential.

Is it beneficial to have two gym sessions per day? I am willing to put in as many hours in the gym as need be as I don't have much else to do during the day but unsure whether "overtraining" is a myth or not. I currently spend around 1 hour per session, should I be spending more time and incorporating more exercises?

My friend offhandedly mentioned that insta-famous fitness girls "probably spend HOURS each day" in the gym to get their physiques and I wonder if I should be doing more?

Thanks for your help.

by marissaxo via Bodybuilding.com Forums - Female Bodybuilding