PCB design - how long should pads be made to hand solder half-vias
I've been using a tried and tested footprint for a mini nRF24L01+ that has edge castellations at 1.27mm pitch.  The pads extend 0.9mm (though rounding up to 1mm wouldn't hurt) and it is very manageable to solder by hand with a small tip.



(Grid = 1mm.)  Here's how it looks in real-life: