If you intend to travel to Ísafjörður by air, you should book your flight to Iceland so that you arrive in Reykjavík no later than the morning of July 26 (Sunday). You will then have time to catch the afternoon flight to Ísafjörður (see also Getting to Ísafjörður).
Similarly, if you are leaving directly after the course, you should not book a flight leaving Iceland any earlier than the morning of August 1 (Saturday). Please note that any overnight stay in Reykjavík is your own responsibility.