Don’t mix apples and oranges!
Work efficiency is objective and it can be measured. Work commitment is subjective and it can’t be measured.
I’d say that you have two professionals at your company and a lot of “pretenders.”
You’re running a business, not an art gallery. This means the “the beauty is in the eye of the beholder” rule doesn’t apply to you as a CEO.
It doesn’t matter when your employees leave in terms of time, but what they leave behind as a result of their work.
Does your business make a profit based on commitment or results and quality? The same applies to your employees. Do they get paid based on their “commitment” or work results?
Those two guys know they did good work. Now, they’re leaving to rest and prepare for the next working day. If they leave every single day at 6 PM and manage to maintain the same quality of work, I really don’t see a problem here.
Other employees can bring sleeping bags to work to impress you, and assure you of their so-called “commitment.” But, ask yourself this simple question as a CEO: What good does it do to my company?
Don’t judge a book by its cover, and don’t judge an employee by their commitment, but only by their results.
You shouldn’t complain even if they leave at 1 PM or 3 PM as long as the work gets done as planned, and you’re happy with the results.
My final and most important advice to you is: instead of checking the time when these two employees leave, you should focus on what other employees are doing during and after regular working hours. I’m sure that you’d be surprised, but not in a pleasant way. And, I’m also sure that you would have a long list of improvements and new demands for these “fully committed” employees.
Think about it, and don’t forget to give a raise to those two employees who leave at 6 PM.