How often does LFR Shipyard mission proc?

[WowIsDead64]

14 days passed - no mission. I need just one last item for my last alt - trinket. The only thing, you can't get via some other means (ring can be crafted). Sub fee runs out today and I have only 9 hours to get it. Mission lasts for 4 hours. How often does it proc? Do I have any chances to get it within next 4 hours?