Estimate time to write an essay by length and speed.
An essay divides into reading, drafting and editing, and the reading is usually the part that overruns. Sources times minutes per source gives it explicitly rather than burying it in a fudge factor. Drafting is length over rate. Editing scales with length and the number of passes, at roughly 1,200 words an hour per pass — slower than reading because each pass rewrites as it goes. Seeing the three separately shows where the time actually sits, which for a well-referenced essay is often more in reading than in writing.
Reading and drafting
Reading hours = sources x minutes each / 60; drafting hours = words / words per hour
Editing
Editing hours = words x passes / 1200
Two is the usual sweet spot: one for structure and argument, one for sentences and referencing. A third pass adds polish but rarely changes the grade band.
Because the plan counts sources rather than minutes. Eight sources at 25 minutes each is over three hours before a word is written, which is why essays started the night before are short on evidence rather than short on words.