The twelve-week year. A 90-day challenge. It seems like even the algorithms of the internet reward you for consistency for 3 months.
Even before I heard of these, when I was busy in my day job, I found that I could cope with long hours and working weekends as long as it was in three-month bursts. I knew that during those three months I had to find a way of making all the things I was currently doing fit into a sustainable timeframe to give me a "break" by being able to work "normal" working hours for the subsequent three months. At the end of the three-month burst, I would be able to take a holiday, get back into a more moderate pace for three months before taking more one on and having a mother three-month burst.
After doing this a couple of times, it no longer took three months to sort out the next big workload. The same techniques can be implemented much quicker once you have practiced them and you start to get into a groove of your own system: cut out these meetings, replace with reports; find out who is reading the reports and cut out the ones not needed; find some areas of the business driving noise and move them to self-serve with a bit of training.
The thing that takes longer than three months is working on yourself. And that is okay. Once you have taken the time to boil things down to habits you can do every day no matter what - then do them every day, no matter what - why stop doing them? Build upon them instead. You might have identified one habit in order to get fitter. Great, well don not stop when you have done this for 90 days, just build on top of it. Find a way of making it sustainable.
Thinking of a 90-day challenge of content creation, I think this is where Gary Vee's document versus create comes from: do not give yourself the excuse of not having ideas for content, just document your day - that is the content.
Where else can you find excuses and turn them on their head? Find a way of keeping going longer than 90 days. Use the common three methods eliminate (other busy work), automate (non-important things taking your time), delegate (the tough bits or get help).