Observations of Type Ia supernovae (SNe Ia) in a few hours and days after explosion play an important role in addressing the long-standing issues about the explosion mechanisms of SNe Ia. Discoveries of early-phase blue excess favor the single degenerate channel; while early red colors are evidences of the double detonation scenario. In this talk, I will review recent progress in this field and demonstrate how the Zwicky Transient Facility (ZTF) can extend the single-object analyses to a large sample of infant SNe Ia. I will also introduce the methodology to perform forced-PSF photometry to generate high-quality light curves, which is essential to constrain the first-light epoch. I will end by summarizing what we have learned from the ZTF Year-1 sample and how the results help to refine our Year-2 observational strategies.