Months rather than weeks, and longer where the seller's records are thin. The marginality work usually adds time before the application can sensibly be made at all.
Structure the deal so it can afford to wait
Due diligence sets the pace. Obtaining three years of records from a small self-serve operation, corroborating the revenue against utility and processing statements, and agreeing a price on that basis takes longer than either party expects, and it sometimes ends the deal altogether. Building the forward plan, obtaining quotations for additional equipment and securing letters of intent from prospective commercial customers adds further weeks.
Only then are the purchase agreement, the escrow arrangement and the source-of-funds file ready, and only then does the published consular processing time begin to matter. The structure that protects both sides is a conditional agreement with funds in escrow that returns the money on a refusal and completes on an approval. A seller demanding completion first is asking the buyer to carry every risk.