Is it possible to have two partitions on external drive that is used for time machine backups?
Yes, it is indeed possible.

The easiest way is to start with a clean drive (i.e. containing no data you want to save), and then use Disk Utility to create two partitions on the drive. You can name the partitions so it is easy for you to identify which one is which.

The partition for Time Machine needs to be formatted as "Mac OS Extended (Journaled)" (HFS+).

The Windows drive will usually be formatted during Windows installation.