Guineas are seasonal layers/breeders... Spring thru Fall. When they start laying varies, due to temps/weather/climate, the amount of sunlight they get etc. My older Hens usually start a little later in the Spring than young pullets/1st timers do, but my guess is they should start laying any time soon.
If they are let out to free range, they may already be laying eggs out in the bushes or tall grass somewhere tho. It's not that common for Guinea Hens to choose to lay in nest boxes if they have a choice to find their own private spot, usually in a well shaded place that's secluded and private.