Thats highly variable. Van’s has listed estimated build hours:
RV-3/4: 2000-2200
RV-7/8/9:1400-1500
R-10: 2000
RV-12: as little as 800
RV-14: 1100-1200
Based upon my own experience I’d say those numbers are way optimistic and really only achievable by an experienced builder who sticks strictly to the plans (ie no major mods). Farming out some work, like building the panel, and going QB helps keep the hour total down too, albeit at a cost— trading money for time.
But the build hours are only the workload part of the equation. What really matters is how much calendar time does it take to go from initial order to flying aircraft. Theoretically if you were retired and made building your full time activity (40 hrs a week) you could build any of these in year. I know of several RV-10s built in less than 18 months but that’s definitely the exception, not the rule. A team is potentially going to build faster than a single individual. However, most of us can’t afford to devote anywhere that kind of time to the project. In reality I would say based on anecdotal evidence that the average build time, depending on the airframe, is between 3-5 years. The newer kits have evolved and have improvements, like match drilled final sized holes which speeds things up.
FWIW, from initial tailkit order to first flight for my RV-10 was 8 years 9 months. When I started I was still active duty USAF and had 2 small kids. 2 deployments, retirement and subsequent start of a civilian career, kit delays, kids sports and school events, vacations, and taking a whole year off between the tailcone and wings, etc, etc all added up.