The time range you define it is converted into:
9 50
10 40
11 30
12 20
13 10
14 00
15 50 -
16 40
17 30
18 20
19 10
20 00
20 50 -
21 40
22 30
So that you need to define these different cronjobs:
50 9,15,20 * * *
40 10,16,21 * * *
30 11,17,22 * * *
20 12,18 * * *
10 13,19 * * *
00 14,20 * * *