I thought that was unusual at first, too, but the way the schedule works right now with two yokozuna and four ozeki (and three intra-sanyaku bouts per day), they pretty much have to start by Day 7, so Day 6 isn't all that early.
Edit: Okay, by Day 8 at the very latest, although that would go against their usual habits, too.
If I didn't miss something, the first intra-ozeki bouts in Nagoya this year were on Day 9. There were one yokozuna and six ozeki, so a total of seven, active in that basho. Now after Barutos injury only six remain active. How do you explain that with 7 Y/O it is possible to start the intra-ozeki bout on day 9, but have to start by day 8 at the latest with only 6 Y/O?