The tendency to complete, or at least begin, a task as soon as possible - even at the expense of extra effort.
Etymology: Latin, pre, before, + cras, tomorrow
Procrastination could be part of why I finished my taxes last night (and part of why my Monday word is so often posted on Tuesday).
Precrastination is a term that appears to have been officially used for the first time in 2014, in relation to this study.
In that study, the term is hyphenated (pre-crastination).
Less officially, the term was used in this 1999 newspaper column.
A couple of articles/blogs about that study are here and here.