There is a lot of debate about the length of a web series episodes. It ranges from people that have tried 1-minute episodes to people that make shows that are 1 hour long! I guess it depends on who is making the web series.
The truth is most people agree that somewhere between 5 minutes and 10 minutes is a good mark. Certainly the most successful web series are close to that mark.
So how are you supposed to define how long your episode should be?
The argument for a short episode:
If your show is comedic, targeted to a younger audience, or meant to be watch on the run, then shorter episodes are very good for that. A bit size. If you are doing a show on tips to do something, short is also better. The key about short content is to design it for people and platforms where they are not going to invest much of their attention spam. So make a killer first 10-15 seconds, and make sure to keep people engage for your minute by keeping that energy and stimulation up!
The argument for the long format:
The only way that a long format can stick, other than coming from a big TV network and be available on Hulu, is to have a very well defined audience and for that audience to be willing to sit through an hour or 45 minutes of content. Interview and educational shows that are targeted to a very specific niche. Those web series episodes can hold up to 45 minutes, even an hour. The best way to go about it is to break your show in three of four segments that change the speed of the show. Will help keeps the viewers engaged.
The Real Length of a web series episode.
The truth is that it will depend on the story and your interest as a producer. Some things need 25 to 45 minutes to be said. And that is fine. Somethings can be said in 2 minutes. Start from your guts and follow what the audience asks from you.