------+---------
 time | elapsed
------+---------
12:XX | XX - 30
 1:XX | XX + 30
 2:XX | XX + 90
 3:XX | XX + 150
 4:XX | XX + 210
 5:XX | XX + 270
------+---------
 time | elapsed
------+---------
 7:XX | XX
 8:XX | XX + 60
 9:XX | XX + 120
------+---------
 time | elapsed
------+---------
 9:XX | XX - 59
10:XX | XX + 1
11:XX | XX + 61
12:XX | XX + 121
 1:XX | XX + 181
 2:XX | XX + 241