Just as there can never exist an actual point in space (see this entry) — only an imaginary one — so I can't see how we can have a present point in time. There can be no immediate moment of any duration; if it is infinitely short then it has no span, and presumably doesn't occur. If it has some duration, however short, then it spans more than a single point and so cannot be a precise moment.
For similar reasons a unit of time — say a second — cannot have an absolute start or end; it is indeterminate in length, or it could even be said it has no length at all, though it has an unspecified duration.
