*sigh*
If I submit my form 5 milliseconds before the current second ends, then unless I submit the next one in 4 milliseconds, it will have a different time stamp. If I submit my form 3 centiseconds after the second starts, then I have 7 centseconds before the next time stamp. It's just simple math - nothing complicated. People don't magically submit right at the first nanosecond of a new second each time, so they will very rarely have a full second before the next timestamp.