When I look at a forecast for a specific location it might show, say, 5mm of rainfall at 3pm. Does this mean 5mm in the period up to 3pm or does it mean 5mm in the period from 3pm onwards?

When I look at a forecast for a specific location it might show, say, 5mm of rainfall at 3pm. Does this mean 5mm in the period up to 3pm or does it mean 5mm in the period from 3pm onwards?