[Grammar] Tomorrow I'm going to work...

[Encolpius]

Hello, I am searching for the proper preposition. If I have to start my work at 8 o'clock, can I say: Tomorrow I'm going to work for 8 o'clock. ??? Thanks.

 

[Barb_D]

For a time, it's at.
For a day, it's on.

ON Monday, I have to be there AT 8 a.m.

 

[Encolpius]

For a time, it's at.
For a day, it's on.

ON Monday, I have to be there AT 8 a.m.

Of course I knew on and at, but I wanted to say something different, but I think it does not exist in English at all.