This is mostly up to you. Most podcasters publish on a weekly basis, some once in 2 weeks and a few post daily. It really depends on how long you need to produce something of good quality and that you're satisfied with. If you find it difficult to produce an episode each week, then you can switch to once in two weeks or even posting on a monthly. Quality would always be rated over quantity when it comes to podcasting. Just try to have a pattern as this is helpful to your loyal listeners.