How long to let a concrete walkway cure
That's built as solid as my parents' driveway. As a walkway, I'd say it's solid and probably ready for use now, but curing it for the additional 4 days could make it more durable and less likely to chip and spall later.

A friend's neighbor poured a 3" thick dog run, then let his dog on it the next day. He later poured an additional 3" slab of the same construction, but kept it wet for 10 days. The fresh slab cracked and chipped within 2 years. The cured slab didn't show a mark even 5 years later.