Silver, "Development ore" is the ore that you would mine to develop your mining blocks. So things like your level cuts, this will be more of an exploration and slower process which generates less tons and usually is lower grade since you kind of don't know where the ore starts and stops, so you poke around the edges and try to center the ore in your face. Once the levels are established, you just blast everything in between them using whatever mining method you choose. The idea is that once you're at that point you have a good idea of where the good gold is and the dilution can be kept down, you also use significantly cheaper mining methods than "development".

In narrow vein mining you establish levels and mine the blocks very quickly, you need a dozen or more faces, mininum, at all times. Which means you might have 4-6 development faces at a time and another 8 or 10 stoping blocks where you can draw ore from.

Again, this is at ALL times, year round, month by month. You don't just do all the development first and then all the stoping, you layer it so there is a lot of overlap. If you did all the development first and then the stopes, you would end up in a situation where you got not enough ore at first, then way too much. The key to mining is the utilization of mining equipment and people to ensure a steady flow of ore, not quick fluctuations to satisfy the market.