Is this Modern Greek sentence grammatically right?

[Κορεάνος]

Για ένα μήνα όπου απουσιάζω, αντί για μου θα λειτουργήσει. Θα σας στείλω αύριο το πρωί.
For a month I'm absent (from today), the other one will work instead of me. I'll send you tomorrow morning.

This sentence will be inserted in a game, so I want to hide the other one's gender for the story, if possible.

[Language patzer]

Για έναν μήνα που θα απουσιάσω από την εργασία μου, θα φροντίσω να αντικατασταθώ, ήδη από αύριο το πρωί.

For one month that I will be absent from my work, I'll make sure to be replaced from tomorrow morning already.

Is that what you meant?

[Κορεάνος]

Thanks for replying. I will contact the scenario writer and reply you again.

Besides, I have a personal question about Greek grammar. Is 'που θα απουσιάσω' or 'που απουσιάζω' grammatically right? Can I make only one word follow after 'που'?

[Language patzer]

Actually they are both correct, yes you can say it both ways. Για ένα μήνα όπου απουσιάζω is perfectly fine, just a bit colloquial, that's all!