I don't know of anyone who has gotten sober (that struggled with addiction) and doesn't know how much time they have, be it in days or months or years.
I think Zencat summed it up best- every day sober is worth celebrating. So to borrow an expression that I've always hated 'whatevers clever' - do it!
I did 30, 60, 90 (AA) and then switched to months. I do pull up
AA History Sobriety Calculator from time to time and check my 'balance' cuz sometimes it just feels good to see how many days have ticked by so far but now I really just focus on when I hit the day of the month. I'll be happy when I can change that to what day of the year! :P
FWIW I think addiction and recovery are both a day at a time. I couldn't get drunk today to insure I'd be drunk this Sunday and I don't believe that by staying sober today I guarantee I'll be sober on Sunday. Hence living, drunk/high or sober was/is a 'day at a time' experience.