Champaran HumSafar Express : इन अजनबी सी राहों में, जो तू मेरा हमसफ़र हो जाये, बीत जाए पल भर में ये वक़्त, और हसीन सफ़र हो जाये. - Piyush Singh

As its most of the time punctual, you get ample time at GTL station. Some say, its a boring train because of the wait at GTl for coupling with Prashanti NIlayam. But use the time wisely and smartly. Even chain route takes same amount of time except that instead of being stationary, you will be on the move.
So use the train to Goto a First Show at Chaitanya Thatre (Best in town) or any other theater. Get relaxed and entertained. You can watch the movie, then have dinner in town before coming to the station to board the train. We did it easily and watched Shatamanam Bhavati Telugu movie. Attached our selfie (First Pic) at the theatre.
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may also opt to hire a round trip auto to visit the district famous, ancient Kasapuram Anjaneya Swamy temple (Hanuman Temple). 14 kms oneway.
Second Pic Source: click here
Or just simply stay at the station or inside your coach and take rest or explore the station.