I've heard comments like this in every possible form before---"Once you get out of college and get a job, you won't have time to...", "Once you're at a startup, you won't have time to...", "Once you start volunteering after work, you won't have time for...".

It's nonsense, you make time for what you think is important. I wake up at 5:30 am to train Brazilian Jiu-Jitsu, I read when I'm commuting, I work hard at my startup, I teach a few nights a week. I plan things out ahead of time and stick to my plans. I don't have kids, but when I do I'll adjust my schedule to make sure I can keep doing what I think is important (kids Jiu-Jitsu starts at 5 years old).

I never found the argument that you won't have time to be very compelling. People who complain about not having time seem to usually be the person who is caught up on every tv show and wake up at 9 to get to work at 9:30.

I think the easiest way to build these habits is to make a plan and stick to it. You want to go to the gym? Get up before work and go. Period. If you aren't getting up 40 minutes early to exercise, you're not busy, you're lazy. Being a good parent definitely takes up a chunk of time, but you can always find time.