Howe much postage to send a postcard from US to Canada? As of September 2014, it costs $1.15 to ship a post card  internationally. If it exceeds 4 3/4 inches high or 9 1/4 inches  long, you will be charged the First Class Mail In â¦ ternational price. + 3 others found this useful.
Concrete is never truly done curing, but the minimum wait time should be 28 days. A slab typically cures at least 80% during that time. I suspect the manufacturer is asking you to proceed cautiously to avoid a lawsuit. If you (or your client) can wait that long, then wait the 120 (or more) days. But I wouldn't put any flooring on it inside a month.
Concrete will start hardening in 45 minutes or less in warm weather (in up to 90 minutes in cool weather). But even though the hardening (technically known as curing) process begins quickly, you should leave the posts undisturbed for at least two days after pouring the concrete.