We study the production of Dark Matter (DM) in a minimal freeze-in model during inflationary reheating. We analyze the case where a heavier parent particle decays into DM and a Standard Model fermion in two reheating scenarios: bosonic reheating (BR) and fermionic reheating (FR). We show that for a low reheating temperature, BR and FR scenarios predict different lifetimes and masses for the parent particle when considering potentials with power-law behavior. We highlight how different treatments of the reheating phase and definitions of the reheating temperature in the literature can lead to conflicting conclusions about the relevance of long-lived particle (LLP) searches in testing the freeze-in model. Additionally, we investigate the interplay between LLP searches and cosmological constraints on inflationary models, specifically $\alpha$-attractor E- and T-models. We find that the inflaton potential and the reheating temperature significantly affect the relic density of DM and have implications for interpreting collider signatures and understanding the dynamics of inflationary reheating.