First find the total number of squares Bill's hoard has: 1000 rolls * 300 squares/roll = <<1000*300=300000>>300000 squares
Then find the number of squares Bill uses each day: 5 squares/time * 3 times/day = <<5*3=15>>15 squares/day
Now divide the total number of squares by the number of squares Bill uses each day to find how many days his hoard will last: 300000 squares / 15 squares/day = <<300000/15=20000>>20000 days
#### 20000