Is it all right to stick or drive dowels into concrete that has been placed 60 to 90 minutes earlier when the temperature is about 70 degrees F?
Whether they can be driven in depends on whether the concrete has begun to set. It might be possible to get them in even if the setting has just begun. But whether the concrete has or hasn't begun to set it would be necessary to vibrate the concrete thoroughly in that area to consolidate it around the dowels. This operation would require much care to see that the dowels do not get moved out of position but that the concrete does flow into intimate contact with them. It has been found possible to revibrate concrete satisfactorily up to ages of around 4 hours, and in some circumstances up to 7 hours, when temperatures are about 70 degrees F.