Yes both in a sense, Shotcrete and Gunite are both terms used to describe pneumatically applied concrete. Gunite used to mean just the dry mix method IIRC, where as shotcrete can mean either. So clarification on both their parts would have been nice. When using either method if done properly a couple days should be fine, the reason the dry mix method is used in structural concrete repair alot of times is the control over the moisture level can allow them to "hang" more material at a time. The reason for concrete being considered "cured" at 28 or 30 days is that at that point it has reached about 95% of its maximum strength. In certain cases however it can take longer if special coatings and sealers are applied this however is usually reserved for special applications. Typically the longer it takes to cure the more structurally sound it is. Wet cured Concrete (concrete kept wet during the cure)is usually significantly stronger than air cured though, or the more moisture it starts with the longer the cure the more strength. Temperature also accounts for a large part of this. Seeing as how your in NJ I assume, strength gain in colder temps is much slower 40degree concrete will be 35-38% of its design strength in seven days as compared to 70-5% for 73degree concrete.
Too many variables to properly answer your question, they both could be right but i would find out more. it sounds like the guy with the longer cure time just might know his concrete a little better though. I would opt for quality any day.
