This. For me the secret to actually going from total couch-potato to fit was to exercise every. single. day but Sundays.
I tried 3 times a week or whatever, and every day you'll find some excuse to push exercising to the morrow.
But doing exactly the same routine every day was key. Then the routine evolves with time, but it's almost always the same routine. I started with a few pushups, then added burpees, then I bought some weights and added a few movements, then I started running 300m a day the first week, and augmented gradually until I ran 42 km every single week.
Start with push-ups. They're fast and require nothing but a flat surface. You can always transition to lifting weights later.
Start today, ideally right now. Seriously. It's your only chance. Tomorrow there'll be an even better reason not to.
Don't worry about initial quantity. You can start with two push-ups, that's fine. It'll take ten seconds if as much.
Repeat every day.
When you feel it got too easy, increment by one starting the following day, not at the moment.