how long does lh surge last

Austin • TTC our rainbow baby🌈 with one little angel on earth 👧🏼 and three in heaven 👼🏼👼🏼👼🏼
How many days can your lh surge be positive on ovulation tests?
I have had 3 days of positive testing. We have BD two of them and will try to again tonight for safe measures. 
This is my first month closely tracking and I was under the impression I should only have 1/2 days of positive testing.