Septic design timeline

Planning a new septic system and trying to figure out how long the whole design phase actually takes. Some people say a few weeks, others mention months. I'm not sure what's realistic. Between soil testing, lab analysis, and getting the final documents, how long should I expect to wait? I'd also like to know if there are any common delays that tend to pop up. If you've been through this, I'd appreciate hearing about your timeline and whether anything caught you off guard.