Mmh, I think you should do what you are realistically capable of (including time to rest and time to relax). So I'd stay consistant with the length.
Ultimately the longer, the better but I recommend starting short specially if you don't have a buffer. The reason is, if your readers is used to read long episodes as soon as they get a short one, they will notice and sometime complain about it.
That leaves a bad taste, in other hands, if they are used to have short episodes and sometimes get longer epiosdes, that's a win win, everyone is happy and they won't really expect you to continue on this path.
If you want to do longer episodes from time to time, choose the right moment in your story. For example when the momentum is high, maybe it's good to a have decent lenght for when things is about to go down or when big revelations are showned.
I personally planned to do few special episodes that contribute to the story, I will probably make them longer.