I tested out a map with a units build time on 1 on SCMDraft. When a built the unit, it went practically in a quater of a second. Would anyone explain this?

SCM Draft is 15x faster than the other editors with it's build times, a build time of 0 will crash the game when attempting to create units(except for macs).

It's only faster than StarEdit and StarEdit mods (such as SCXE and FartyEdit.) StarForge has it, too. The reason is that StarEdit divides the value saved in the map by 15. Thus 1 in StarEdit = 15 in the actual map. They will only crash PC users if they are looking when the unit is built (I cannot remember if that applies to having a barracks, for example, selected when building.) If you are building with, say, a probe and cannot see it actually building it will not crash. This can be useful in very specific circumstances, but generally it is wide to avoid 0 build time altogether (except for upgrades, of course. They will always work with 0 build time.)
Also, last I checked, you cannot build zerg buildings with 1/15th build time. They will sit indefinitely unfinished.