This study has revealed critical facets of polymer crystal nucleation under high-driving force, long-chain conditions. First, the exothermic nature of polymer crystallization and variations in system densities during early-stage polymer crystal formation do not substantially influence structural properties of early-stage polymer crystal nuclei, though they are likely relevant to longer-time kinetics and thus rate estimates. Second, this study has demonstrated that high-driving force, long-chain crystallization (particularly nucleation) can be faster than chain-level relaxations, and can occur without substantial chain-level conformational changes. There is thus a separation of timescales during high-driving force crystallization in entangled polymer melts. The concept that local structures and environments guide polymer crystal nucleation processes connects the two aforementioned insights, and it appears that local rearrangements occur such that local orientational ordering precedes densification, though much work is still needed. The microscopic details of polymer crystallization processes under high-driving force, longchain conditions are of great industrial relevance, and their further elucidation at the molecular-level will advance attempts to control and understand polymer processing.