My thanks go to iqbaliqbal on Health Unlocked for this post:

Natural history of motor symptoms in ... - Parkinson'''s Movement

This links to [1].

We normally think of levodopa as having a short term impact of less than a day. (When combined with carbidopa its half-life is about 90 minutes.) Dotted around the levodopa literature are claims that there is also a long duration response, measured, perhaps, in weeks. This paper is the most convincing one that I've come across:

Celia et al. report:

"we found a sustained LDR 7 days after of withdrawal in patients with a 15-year history of Parkinson's disease, with UPDRS-III scores still 32-55% better than the baseline ... despite the 3-5 years elapsed from the baseline assessment. On the other hand, temporary withdrawal of levodopa for time intervals longer than 15 days, 8 years after the onset or for just 7 days after 20 years of Parkinson's disease, was associated with return of motor performance similar to baseline. "

Reference:

[1] "Natural history of motor symptoms in Parkinson's disease and the long-duration response to levodopa"
Roberto Cilia et al.
Brain, Volume 143, Issue 8, August 2020, Pages 2490-2501
Natural history of motor symptoms in Parkinson’s disease and the long-duration response to levodopa | Brain | Oxford Academic

John