I've been playing with this a bit and sadly I don't think this is possible in a single task. ePO uses the Quartz scheduler syntax, which does not appear to let you specify multiple entries in the "Xth day of the week" field. You might need to set up two tasks, one for the first thursday and one for the third:
Don't forget, when your helpful posts earn a kudos or get accepted as a solution you can unlock perks and badges. Those aren't the only badges, either. How many can you collect? Click here to learn more.
Community Help Hub
New to the forums or need help finding your way around the forums? There's a whole hub of community resources to help you.