I bought t4 today (as can be seen in pic) in the name of Science.
120 Towers done for t4. 8 more sigils, so thats 32 more towers min, depends on ravens.
So everyone in the guild buys t4 for the event, it will finish. Thats providing everyone in the guild is able to buy t4 and arent busy all weekend, as lets be honest a lot of people have shit going on on weekends.