Which One Should Be Used?
'On' and 'for' both can be used to show time as they are prepositions of time.
Indicating The Amount of Time
'For' is used to show the amount of time an action took. For a example:
He hasn't called us
Indicating The Time of Occurrence
We can use 'on' to show when an action or event happened. Have a look:
My birthday is
She had several traumas
Are They Interchangeable?
The answer is no. We cannot replace 'for' and 'on' as the meaning will change completely and it will confuse the audience.
For and On in a Sentence
We can use 'for' and 'on' in one sentence to give more detail about the time.
I will see you
The movie will premier
Indicating an Exact Time
We use the preposition 'at' to show an exact moment in time. Have a look:
He will pick me up
She will see you