  Decades long monitoring of millisecond pulsars, which exhibit highly stable
rotational periods, in pulsar timing array experiments is on the threshold of
discovering nanohertz stochastic gravitational wave background. This paper
describes the Indian Pulsar timing array (InPTA) experiment, which employs the
upgraded Giant Metrewave Radio Telescope (uGMRT) for timing an ensemble of
millisecond pulsars for this purpose. We highlight InPTA's observation
strategies and analysis methods, which are relevant for a future PTA experiment
with the more sensitive Square Kilometer Array (SKA) telescope. We show that
the unique multi-sub-array multi-band wide-bandwidth frequency coverage of the
InPTA provides Dispersion Measure estimates with unprecedented precision for
PTA pulsars, e.g., ~ 2 x 10{-5} pc-cm{-3} for PSR J1909-3744. Configuring the
SKA-low and SKA-mid as two and four sub-arrays respectively, it is shown that
comparable precision is achievable, using observation strategies similar to
those pursued by the InPTA, for a larger sample of 62 pulsars requiring about
26 and 7 hours per epoch for the SKA-mid and the SKA-low telescopes
respectively. We also review the ongoing efforts to develop PTA-relevant
general relativistic constructs that will be required to search for nanohertz
gravitational waves from isolated super-massive black hole binary systems like
blazar OJ 287. These efforts should be relevant to pursue persistent
multi-messenger gravitational wave astronomy during the forthcoming era of the
SKA telescope, the Thirty Meter Telescope, and the next-generation Event
Horizon Telescope.
