The Montblanc caliber 4810-503 is based on the ETA/Valjoux caliber 7753. This caliber number was recently updated to MB 25.02.
Not a 7750
You may see many bloggers or watch sellers incorrectly listing the base as an ETA 7750. The difference, which makes for the signature styling of the Montblanc Timewalker featuring this movement, is the placement of the subdials. The 7753 has the subdials at 3, 6, and 9. Another differentiator is that there is date pusher on the side of the case at 10:00. This is why the Montblanc Timewalker includes a special pusher tool. If the movement were based on a 7750, it would be possible to set the date via the crown.
Montblanc 4810 503 vs ETA 7753
Montblanc made a few changes to their caliber 4810 503 compared to the standard ETA 7753. In most timepieces with the 7753 you will find the date at 6:00, however, Montblanc fit the date between 4:00 and 5:00.