How long-16 years
How l stayed motivated- I didn't. Call it 10 years on, 5 years off, 1 year on, 1 to go.
Early on, we hit it pretty hard but I would say I lost some focus when we had kids. Partially as a result of work and home related stress (I needed to have some fun/distraction!) and also the plan was different back then. My wife was going to go back to work full time and let me switch out being a stay at home dad, although the kids were in school so it would have been 80% ER and 20% SAHD with no reliance on investment income. Our portfolio had hit the mark determined to be enough for full retirement at 55, so I endulged some hobbies, convieniences, and luxuries.
Fortunatly, I never stopped maxing out the retirement accounts and there was still leftover taxable dollars for investment as well. The good habits formed in the first 10 years stuck and our net worth continued to grow despite inattention. All said and done, we probably had around $1000/mo in non-essential excess spending, but almost all if it was descretionary as we did not upsize the house, cars, or other fixed expenses.
When my wife's full time prospects fizzled due to budget cuts, we had to buckle back down and rework the numbers to keep ER a reality. Looking back, I don't regret the spending much, I had a good time, and bought a bunch of durable tools etc that will support post ER hobbies, saw how the other side liveed a bit, and was able to relax a bit, thereby avoiding frugal fatigue.
Now the budget is pretty tight, so tight that I don't think I could have survived the early childhood years plus five stressful years at work with the added stress of pinching every penny. Right now I am motived in a hair on fire kind of way becasue my fire hose of cash is about to be turned off!