Hi
The eggs could be fertile for up to a couple of weeks I believe, but if you are hoping for the hens to rear them, you would need at least one of them to go broody. At this time of year within the limited time frame you have, that is unlikely.
Purchasing an incubator and brooder is expensive when you have no guarantee that the eggs are fertile. Running with a cockerel is no guarantee that they will be. My main man is not feeling/acting as virile as usual as he is moulting which is common at this time of year and it will depend on how many hens were in with the rooster when you got them as to how many he might have serviced. Assuming you have the space to raise them indoors until they are old enough to survive without heat, integrating the chicks into your existing flock can be difficult and stressful and you need to be able to monitor them through the day to ensure they are not getting picked on.
You also need to consider whether you have the space in your coop/run for more adult hens and what you will do with the roosters that hatch. Also, if you incubate and raise them in a brooder, what happens if you only have one hatch and it is on it's own all day. At this time of year it will be difficult to buy some playmate chicks and trying to integrate a single youngster into an existing flock of adult birds is VERY difficult, possibly deadly.
I would suggest you only go for it if one of the hens turns broody and that way you have no additional outlay and storage of equipment, no real worries with keeping them warm and flock integration and the decision is in the lap of the gods.
Best wishes
Barbara