This is going to vary wildly by manufacturer. If you’re talking about a DIY Weld Table kit, WeldTables.com quotes 4-6 weeks. WeldProjects.com and Texas Metal Works quote 2-3 weeks.
Both manufacturers offer designs that have tabs and slots to make assembly easier with parts generally snapping together. Only WeldProjects and Texas Metal Works have self-fixturing components to allow the kits to be assembled with bolts and capture nuts. Here’s a video demonstrating assembly:
