The length is set by three things: how big the commitment is, whether the person you are talking to can actually sign, and how disruptive the transition looks from their side. A deal that involves changing a phone system and migrating a file server is a bigger act of trust than one that does not, and it takes longer for reasons that have nothing to do with your selling.
The mistake worth avoiding is having no stages. Without a model of what should happen at each step and roughly how long it takes, a deal that is progressing normally and a deal that has quietly died look identical — both are simply "still open". A handful of named stages with a rough expected duration turns that into a question you can ask.
And a long cycle is not a signal of a large deal. More often it means the person who can say yes has never been in the room. Deals that drag are usually waiting on somebody who has not been engaged, and the fastest way to shorten a cycle is to get higher up rather than to follow up more often.