Five minutes can average from 2-3 paragraphs, about 250 words. It might be that's all you have time for. Then again, maybe now you feel able to carry on and finish your thought.
It doesn't even have to be good writing. It could be absolutely terrible. Now, it may be that you're the kind of writer that requires every word to be perfect before you move on. So, after five minutes, go back and clean up your work, which is cool too since a lot of writing is rewriting anyway. But, the point is you started and maybe this is the beginning of a new habit if you keep it small and manageable.
Just give yourself five minutes.
PS> 250 words just happens to be the daily word count for the BSFW Daily Writing Challenge. BSFW members can message Brad on the meetup sight and he'll add you to the list. If you're not a member, then join us.