Full Idea
There seem to be three possible ways for time to be fine-grained. The ordering of instants could be discrete (like the integers), dense (like the rational numbers) or continuous (like the real numbers).
Gist of Idea
Time could be discrete (like integers) or dense (rationals) or continuous (reals)
Source
Katherine Hawley (How Things Persist [2001], 2.5)
Book Reference
Hawley,Katherine: 'How Things Persist' [OUP 2004], p.51
A Reaction
She seems to assume that time must be 'grained', but I would take the continuous view to imply that there is no grain at all (which is bad news for her version of stage theory).