Millisecond pulsar (MSP) timing — the process of accounting for every rotation of a rapidly spinning neutron star over long time spans — is a powerful tool for probing realms of physics that are otherwise inaccessible to Earth-based scientists. In this talk, I will discuss how the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) pulsar timing array uses MSP timing observations for the detection of low-frequency gravitational waves. Additionally, I will discuss our use of relativistic Shapiro delay measurements to precisely determine MSP masses. Of particular interest is J0740+6620, one of the 70+ MSPs timed by NANOGrav. By combining NANOGrav observations of this source with orbital phase-specific observations near conjunction using the Green Bank Telescope, we measured the pulsar’s mass to be ~2.14 ± 0.09 solar masses. Additionally, recent high-cadence observations with the Canadian Hydrogen Intensity Mapping Experiment have resulted in an improved mass uncertainty. The measurement of such a massive neutron star is helpful in constraining the poorly understood neutron star interior equation of state.