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The bus services is maintained by UPSRTC. I know it is real trouble for people who are looking for bus time schedule between agra and noida and vice versa, because no exact information is available online. To find out this i went to their website of UPSRTC and found nothing exactly.
For correct information it would be good if you contact them via phone or visit a nearby Bus Adda(bus stand). According to the guard at Parichowk, bus service starts from Noida Sector 35 Bus Stop, bus heads towards Parichowk and then towards Agra via Yamuna Expressway.
Rough Schedule -
7:00am from Parichowk and then almost every half an hour from parichowk according to the guard.