If your urban bench just arrived, the most realistic answer is 45 to 90 minutes for the bench itself. That is the typical range for a flat-packed or semi-assembled park bench with pre-drilled holes, standard hardware, and a basic set of instructions. Some simple two-seat metal-and-wood benches go together in 30 to 40 minutes, especially if you have a helper and use a cordless drill with the right hex bit. Heavier cast-iron or steel benches with backs, armrests, and a lower brace can take closer to two hours the first time you build one.
One thing that surprises people is the difference between assembly and installation. You may bolt the bench frame together in half an hour, then spend another 45 minutes placing it, leveling the feet, and anchoring it to concrete or pavers. If the bench is surface-mounted and will be secured with expansion bolts, drilling into hard ground can add significant time. If it just sits on a firm surface, you are done much sooner.
Your experience level matters, but not as much as your preparation. I always recommend unpacking everything, grouping the bolts by size, and checking the parts list before picking up a tool. That five-minute step prevents most mistakes that eat up time later. Using the wrong fastener in an end cap and having to take it apart is what turns a one-hour job into a three-hour job.
Working alone is also slower. You can absolutely assemble an urban bench by yourself, but you will need to prop up one end while aligning the opposite side. A second person makes a big difference because they can hold the legs steady while you insert bolts through the seat slats and backrest brackets. With two people, most urban benches go together in under an hour. Alone, plan for 90 minutes on average, and possibly longer for a heavy iron bench.
Tool choice is another variable. A basic hex wrench will work, but it is slow. A cordless drill or impact driver with hex and socket bits speeds up the job considerably. A ratchet set helps with locknuts and dome bolts. A rubber mallet can help seat wood or recycled plastic slats without gouging the finish. If the bench has cast-iron ends, avoid over-tightening because they can crack or chip.
So, if you are asking for a safe block of time, set aside two hours from box to finished bench. Most people finish in 45 to 90 minutes of actual assembly, with another 30 to 60 minutes if installation requires drilling into masonry. If the instructions are clear, the parts are intact, and you have a helper, you will probably be sitting on the bench testing it before your coffee gets cold.