A prepared company typically runs six to nine months from engagement to closing, and preparation before that commonly takes another six to twelve. Unprepared companies take longer or do not close.
More detail
The phases are reasonably predictable. Preparation and financial clean-up comes first, and it is the phase owners are most tempted to skip. Then materials and buyer outreach, usually four to eight weeks. Then management meetings and indications of interest, then a letter of intent, which typically grants the buyer 60 to 90 days of exclusivity. Diligence and documentation run in parallel during that window: quality of earnings, environmental, legal, insurance, customer calls where permitted, and negotiation of the purchase agreement. Deals slow down for predictable reasons: financials that will not reconcile, a surprise in the environmental report, a customer contract nobody could find, or a seller who is not emotionally ready to sign. The first three are solvable in advance.