The Hubble constant at the present epoch (H_0) is an important cosmological parameter on which all extragalactic distances depend. Multiple approaches need to be pursued to constrain its value in order to be able to identify and eliminate unknown systematic errors present in any one approach. Strong gravitational lensing offers one method to constrain H_0 free from calibrations associated with standard candles. It is based on (i) measuring the time delay(s) between the multiple images of a cosmologically distant variable source which is strongly lensed by a galaxy or galaxy cluster that lies in close proximity to its line-of-sight and (ii) modelling the mass distribution of the deflector. We have carried out photometric monitoring of a sample of six gravitationally lensed quasars using the 2-m Himalayan Chandra Telescope (HCT) as part of the COSmological MOnitoring of GRAvItational Lenses (COSMOGRAIL) campaign to measure time delays of most known lensed quasars in both hemispheres using a network of medium-size telescopes. I will discuss in detail our results of this campaign, using a newly devised "difference-smoothing" technique to measure time delay and pixellated modelling of the mass distribution of the deflector to constrain the H_0 value. Further, I will also highlight the usefulness of our time delay measurement technique to other AGN monitoring programs, such as reverberation mapping, often used to infer the kinematics of central regions of AGN using 1-2m class telescopes.