My take

You will get some RPM based answers and they would be good..but my personal take on this has been very crude...

You need to handle the bike like your girlfriend...You need to keep pushing till you know that the bike is not liking it..if you change the gears too quick, neither of you will enjoy the ride..not you and not your bike...
If you push too hard, it will damage the engine...(Indian bikes are not made for too much Stress...Specially Bajaj)

So take your time and experiment and find your own sweet timing when you and your bike would feel the most comfortable and you still enjoy the ride...
Cheers