Stumbled across this article discussing how much of Trump's presidency he has spent Tweeting. It has an interactive graph that you can manipulate based on long long you think it takes Trump to Tweet out an original Tweet as well as how long it takes for him just to retweet something. My estimates below (your results may vary).
If it takes Trump 4 minutes, 13 seconds to write a normal tweet and 6 seconds to retweet, we can estimate that:
Trump has spent 41 days, 2 hours and 56 minutes tweeting since taking office, with 12 days, 1 hour and 42 minutes of that occurring during work hours.
Of that, 40 days, 20 hours and 23 minutes was spent tweeting original tweets.
Trump spent the most time tweeting in October 2019, when he spent 3 days, 0 hours and 6 minutes on it. That was also the month he spent the most time tweeting during work hours, 20 hours and 27 minutes in total.
https://www.washingtonpost.com/politics/2020/05/12/how-much-trumps-presidency-has-he-spent-tweeting/