Delayed opening port assembly

A port sub connectable to a downhole tubular, the port sub comprising:

• a wall defining an inner bore and having a flow port extending therethrough;
• and
• a port assembly partially or wholly positioned in the flow port, the port assembly comprising a burst disk adjacent the inner bore and a dissolvable barrier spaced apart from the burst disk to define a cavity therebetween and positioned further away from the inner bore than the burst disk, the dissolvable barrier having defined therein a plurality of holes to provide a plurality of thinner areas in the dissolvable barrier,
• wherein, when the burst disk and dissolvable barrier are intact, the burst disk and the dissolvable barrier block fluid flow through the flow port,
• wherein, when the burst disk is ruptured and dissolvable barrier is broken through at least one of the plurality of thinner areas, the ruptured burst disk and broken dissolvable barrier provide a flow passage to permit fluid flow therethrough, and
• wherein the dissolvable barrier is configured to be broken through after the burst disk is ruptured and after a breakthrough time has lapsed.