10. Prepositions of time
Before at a point of a time
Before 20th April for a 20% discount – you will not get a discount
after 20th .
Until/till to talk about a period of time up to a point of
time
the museum will be open until 10pm – after 10 pm will be closed
By to talk about a single event happening at or before a
period of time
We need to open the museum by 10 am – visitors expect to enter
at 10 am
For to talk about periods of time
There will be longer hours for 3 months .