Add 12 and 16 female pin headers with the female side facing upwards on the Feather M4 Express board. This will let us plug the RTC above.
The large headers will allow more room for the JST connector and lipo battery to fit between the RTC and Feather board.
Use a small amount of tac to hold the headers in place. Make sure the headers are flat against the board and then solder each pin.
We can use a Panavise to hold the boards while soldering.
Use the header pins that came with RTC. Insert the headers with the longer pins facing downwards like shown in the picture.
You can use flush diagonal cutters to cut one of the headers to fit inside on the 12 pin side of the board.
Solder the short feather headers underneath the board with the female ends facing downwards like shown in the picture.
Once all of the headers are soldered on, we can stacking them on top of each other.
Add a coin cell battery to the RTC board by sliding it in with the + side up and at an angle.
There is just enough room to insert the lipo battery between the Feather M4 and the RTC board. Carefully coil the wires so they fit between the boards.
Align the stack of boards with the cutouts on the 3d printed case. Slip the board stack inside the case and attach the watch bands.
The end stoppers on the bands fit inside the slots on each side of the case.
Putting the watch on with one hand can be tricky if you don't clean off the retraction left behind after 3d printing the case. Use a flush diagonal cutter to clean the adjustment holes and buckle tongue.
If the watch doesn't fit, you'll only need to adjust the watch bands by editing the length parameters available in the source files.