Along with the inherent complexities of seed and dormancy, the use of different genotypes or mutants to study the molecular mechanisms underlying seed dormancy leads to potential biases and data misinterpretation. To provide a comprehensive insight into the actual protein activities involved in seed dormancy establishment, a SWATH-MS proteomics was performed on dormant and non-dormant developing seeds of Xanthium strumarium at five consecutive time intervals including three, 10, 20, and 30 days after burr emergence and full maturation. The amount of approximately 3.5% differentially abundant proteins (DAPs) with a ~94% stage-specificity supports considerable proteome overlap in the two seed types. More than 38% of all differentially abundant proteins were observed at the first stage, supporting the importance of this stage of seed development for seed fate determination. Rapid overrepresentation of proteins responsible for cell wall biosynthesis, cytokinesis, and seed development were detected for non-dormant seed at the first stage, while dormancy-associated proteins showed less abundance. In the middle of seed development, we identified DAPs involved in seed maturation and ABA signaling. Interestingly, higher abundant proteins in the mature non-dormant seed were mainly involved in the facilitation of seed germination. Taken together, the temporal pattern of the accumulated proteins demonstrated a delay in the initiation of active cell division, enriched response to ABA, and defect in the seed maturation in developing dormant seeds. Moreover, stored proteins in the mature dormant seed are responsible for delaying germination but not dormancy induction. Finally, assume that dormancy may be established at a stage of seed development earlier than previously thought.