The traffic lights at three different road crossings change after every 48 seconds, 72 seconds and 108 seconds respectively.

We find the LCM of 48, 72 and 108 first to get the time after which they will blink together again. 

Hence, LCM $=2 \times 2 \times 2 \times 2 \times 3 \times 3 \times 3=432$

So, they will blink again at 432 seconds past 8:00 am

or, $\frac{432}{60}=7$ minutes and 12 seconds past $8: 00$ am

So, the time will be 08:07:12 hrs