If you’re working full time you might have to get up every day at five a.m. to fit your training in, and this will take commitment, motivation and determination. It won’t help if after a few weeks you revert to your former habits, and get up half an hour before you have to leave for work.
Whether it is getting up early, or beginning a fitness program your motivation and commitment needs to last over the long term to have an affect. In training for a marathon it will not help running for ten miles every two weeks, and doing no exercise in between. Your body will have forgotten what it has to do by the time you run again!
It is better to run three or more times a week with one longer run on the weekend, and you will be in better shape.
These small, regular runs will add up to success over time, but they are far easier to do when you have a target to aim at. This can be a time you want to run, or the desire to complete the 26 mile race. Either way if you know what you want to achieve you will be more likely to do the things you need to do. Having a target concentrates the mind, and increases your motivation.