You should probably ask. The plans will tell you what the PSI should be, usually 2500 - 3500. The concrete guy could up it to 4500 or higher at no extra cost if he wants to beat the rain, however, with the faster set time comes the possibilities of finishing issues. More importantly, you need to ask about an accelerant: they're not used often (usually only in situations were you have freezes) because improperly used admixes can affect structural strength (something that's more critically important with structural slabs or precast structures) but you can never be too careful about contractors taking shortcuts.