Preimplantation development of mouse oocytes fertilised in vitro was assessed in a non-humidified incubator with time-lapse cinematography (CCM-iBIS). The developmental rates of embryos to the 4-cell and blastocyst stages under 5% CO2, 5% O2, and 90% N2 in CCM-iBIS were significantly higher than those under 5% CO2 in air in CCM-iBIS and a conventional CO2 incubator (CPO2-2301). The developmental speed of embryos was much faster in those cultured under lower oxygen tension in CCM-iBIS than in higher oxygen tension in CCM-iBIS and CPO2-2301. Embryonic development was much faster and more synchronised under lower oxygen tension. Non-humidified culture did not affect the development of the embryos. Mouse embryos cultured at lower oxygen tension reached 2-cell at 17 h, 3-cell at 39 h, 4-cell at 40 h, initiation of compaction at 58 h, morula at 70 h, and blastocyst at 82 h after insemination on average. Although compaction partially unravelled with cell division in compacting embryos, it appeared to complete depending on the timing of observation. Observation at a conventional 24-h interval 13 likely misjudges the developmental rate to morula. Determination of embryonic development 72 h after insemination may be more appropriate for “compacting morula” rather than “morula” in mice.