Music variations from a source theme (8-bit style)

Hi!
For a personal project, I need a variation on this 1986’s video game theme: https://www.youtube.com/watch?v=9WgAitWll_g
The idea would be to make it quite similar, but different enough to have its own identity. Perhaps a slight melody variation would work.
The sample provided is a single long track, but the deliverable should be divided into these themes:

- Ingame (0:14) - 45 seconds
- Boss Level (2:27) - 45 seconds
- Game Over (6:07) - 4 seconds
- Main Menu/Pause (a short percussion loop in the same overall mood would do).
Can you estimate the hours required for this comission?

Thank you in advance!