The composition and properties of potatoes have been comprehensively studied; however, effects of different cultivation periods on these factors remain unclear. Hence, we aim to provide insights for cultivating potatoes with desirable properties by controlling the potato growth time and cultivars. Physico-chemical quality characteristics of three potato cultivars—Chubaek, Superior, and Atlantic—were analysed at different cultivation periods (80, 90, and 100 days). Regardless of cultivation period, total starch and amylose content of the cultivars was as follows: Atlantic > Superior > Chubaek, whereas sucrose and glucose content was in reverse order. The Atlantic cultivar showed the highest dry matter content, whereas Chubaek showed the highest moisture content. In all cultivars, glutamic acid and aspartic acid were the predominant amino acids. Peak viscosity was the highest in Atlantic cultivar and increased as the cultivation period progressed. Final, peak, and breakdown viscosities were positively correlated with starch and amylose content and negatively correlated with glucose, sucrose, and most amino acid content. Hierarchical clustering heatmaps showed that all three cultivars cultivated for 100 days exhibited different patterns from those cultivated for 80 and 90 days. Overall, quality characteristics of the potatoes were more influenced by genetic characteristics than by the cultivation period.