It come on the same time evey month

Depends on how on time your period is. Mine was always the same day each month, really easy to keep track of, when I was 1 day late I took a test and found out I was pregnant. But if your period isn't that consistent 5 days is normally good.

Okay thanks cause she miss her period today nd she always on time

Some tests can show before you miss your period. But I'd say at least 3 or 4 to be safe.