Inconel 718 (IN718) is a Ni-based superalloy that must undergo heat treatments (HTs) to achieve desired microstructure and properties through precipitation hardening. When produced by additive manufacturing (AM), this alloy does not respond to the established HTs in the same way as conventionally produced IN718, and there is still no consensus on which routine yields the best results. This work aims at providing a fundamental understanding of the HT response of laser powder bed fusion (PBF-LB/M) IN718 by continuously monitoring the microstructural evolution via time-resolved synchrotron X-ray diffraction (beamline ID22 of the European Synchrotron Radiation Facility, ESRF), complemented by post-mortem electron microscopy (EM). Two different scanning strategies were used, leading to different as-built states. The HTs consisted of a single-step solution annealing (SA, 1 hour) plus a single-step aging (5 hours). Two SA temperatures, SA1 = 1020 °C and SA2 = 1080 °C were tested; the subsequent aging treatment was always fixed at 760 °C. Qualitative examination of the results indicate that SA2 was more effective in promoting the dissolution of Laves and chemical homogenization. In addition, SA1 induced the precipitation of the generally detrimental δ phase after only 15 minutes at 1020 °C. Due to higher availability of Nb in the matrix, samples solutionized at 1080 °C exhibited higher amounts of γ” after aging, when compared to those treated at 1020 °C.