can i walk on concrete after 4 hours

For sure, that totally depends on the context. Are you asking about walking on a concrete floor after it's been laid out and waiting for 4 hours?

Technically, you should wait for at least 24 hours to ensure that the concrete has started curing and is hard enough to walk on without damaging the surface. Four hours might be too soon and you could end up harming the concrete finish or, even worse, sinking in and getting stuck!

It's not recommended at all but if you absolutely must, try to distribute your weight evenly across a larger surface area to minimize the potential damage to the still-wet concrete. Like, you could use pieces of plywood to step on. But again, try to avoid walking on fresh concrete before 24 hours pass if possible!