As it happens, I've read most of the TPR interviews (and extracted ~187 preferred writing times so far), as well as a parallel interview series run by GoodReads, and looked at/run various polls: https://www.gwern.net/Morning-writing
TPR interviews some rather strange and obscure writers, and overall they don't seem to be particularly anomalous. The overwhelming majority of writers, whether fiction or nonfiction, do seem to write in the morning, although it seems that younger and nonfiction types may be somewhat more likely to prefer later starts or writing in the evening.
(Samuel R. Delany, for example, whose interview I read the day before yesterday, reported in 2011 that he always gets up at 5AM to do his writing now, but as a young man he started later in the morning - similar to other reports by elderly writers contrasting their youthful later-timed writing to their present early-morning writing, describing themselves as no longer having the energy to write all day, which makes sense given the lifetime shifts in chronotypes from owl to lark and the difficulty of the elderly in sleep. And shades of OP, a decent number of afternoon/evening writers say something along the lines of 'I would write in the morning-afternoon while the kids were at school, but now that they're grown, I can write later in the day.')
TPR interviews some rather strange and obscure writers, and overall they don't seem to be particularly anomalous. The overwhelming majority of writers, whether fiction or nonfiction, do seem to write in the morning, although it seems that younger and nonfiction types may be somewhat more likely to prefer later starts or writing in the evening.
(Samuel R. Delany, for example, whose interview I read the day before yesterday, reported in 2011 that he always gets up at 5AM to do his writing now, but as a young man he started later in the morning - similar to other reports by elderly writers contrasting their youthful later-timed writing to their present early-morning writing, describing themselves as no longer having the energy to write all day, which makes sense given the lifetime shifts in chronotypes from owl to lark and the difficulty of the elderly in sleep. And shades of OP, a decent number of afternoon/evening writers say something along the lines of 'I would write in the morning-afternoon while the kids were at school, but now that they're grown, I can write later in the day.')