We present the commissioning results and first scientific observations from the newly installed TWIST (TWenty Inch Survey Telescope) observatory ─ a 50 cm telescope equipped with an sCMOS (scientific complementary metal-oxide-semiconductor) camera providing a $36.1\times 24.1$ arcmin$^2$ field of view ─ housed in the former enclosure of the Super Wide Angle Search for Planets-North (SuperWASP-North) facility. We conducted a 67-night, 199-d baseline white-light monitoring campaign centred on the globular cluster M3 aimed at characterizing stellar variability within the cluster while also assessing the photometric performance of the newly commissioned system. We report the discovery of four new SX Phoenicis variables (V301─304), confirm their cluster membership, and identify fundamental-mode pulsation in one, allowing an independent period─luminosity-based distance estimate to M3. We revisited 231 previously known RR Lyrae stars, providing updated period measurements for 203 and white-light amplitudes for 198. We detected Blazhko-like modulation in 53 stars and characterized the modulation parameters for 28. Notably, we measure periods and amplitudes for the unclassified variables V286 and V287 for the first time. We also identify three foreground flaring M dwarfs, and assess the feasibility of detecting microlensing events in M3, concluding that expected rates are negligible. Alongside the scientific results, we introduce a new correction technique for flat-field images affected by scattered light and present a full characterization of the observatory's photometric capabilities. These results demonstrate the scientific utility of TWIST for high-cadence time-domain surveys using modest-aperture instrumentation.