I added pauses at the following layers to insert the magnets:

• Top: 24.2mm (Layer 121 at 0.2mm layer height)
• Bottom: 8.4mm (Layer 42 at 0.2mm layer height)

The design is optimized for 5mm cube magnets. I recommend this pack on Amazon, which includes enough magnets to create 30 cubes.

If you’re printing multiple blocks simultaneously, be prepared to manage the magnetic forces while inserting the magnets during the pauses—it can be a bit tricky as they tend to attract each other!

I've provided the STEP file so you can adjust it to fit your desired magnet size. Be sure to use a cube magnet and set the offset to leave enough space for the magnet to rotate when placed against another magnetic block.