i use to set a time, typically in the evening e.g 8pm, i would write because i mainly had essays to write about 100 words and would sit there until i got 100 words, sometimes it took like hours and sometimes only minutes but as long i hit my word count. i feel if you get a word count goal even if you write utter shit, you still technically did something that day.
it must of work because I've graduated now lol.