The FCC today once again altered the bidding rounds structure for its ongoing AWS-3 spectrum auction.

Starting tomorrow, the auction will shift to 14 ten-minute rounds each day, reducing the total bidding activity time to two hours and 20 minutes daily. The new rules come just days after the FCC changed the schedule to ten 15-minutes rounds each day, or two and a half hours total.

The FCC warned bidders to be vigilante under the new schedule.

“With these short bidding periods, it is essential that bidders have firm back-up arrangements ready for immediate implementation,” the FCC wrote in an announcement.

The rounds are getting shorter and increasing in frequency as the AWS-3 auction grinds on at a snail’s pace. The just-completed Round 175 pulled in $3.4 million in new bids, enough to represent of 0.01 percent increase of the total revenue that now sits at $44.6 billion.

AT&T, Dish Network, T-Mobile and Verizon are all bidding in the auction. The auction will continue until new bids stop coming in.