9 hr * 60 min/hr = 540 min.
540 min * 60 sec/min = 32,400 sec.
Use the method described by panic mode: round the number down until there is only one non-zero digit left. Here, 32,400 rounds down to 30,000.
Now count the number of zeroes; the result is the order of magnitude: 4.
(You see this in scientific notation also: 30,000 = 3 × 10^4.)