Suitable cotton variety selection is imperative to cope with temporal variations for yield enhancement and sustainability under unpredictable climatic conditions. Cotton varieties including transgenic (Bacillus thuringiensis) and non-transgenic (non Bt.) were sown from 10-March to 21-June with 20 days interval for two growing seasons (2012 and 2013) consecutively while cotton sowing after wheat harvest is normal practice at farmers' field in Cotton-Wheat cropping system of Punjab-Pakistan. Phenology, growth indices, seed cotton yield (SCY) and its heat use efficiency of varieties were estimated on daily basis by using statistical models. Seed cotton yield (SCY) was significantly correlated with crop duration exhibiting delays in planting (21-June) impact on shortening of phenophases i.e. first square, flower, boll initiation and boll opening by 8, 7, 4 and 6 days, respectively compared with 10-May planting in first season while second season advanced 0-3 days owing to deviation in frequency of cold shock <11 °C and heat stress >35 °C. Long crop cycle varieties AA-802 and IR-3701 took 6-9 days more compared to short season NIAB-112. More heat units accretion 46, 33, 20 and 13 % to switch into next phenophase (first square, flower, boll initiation and boll opening) was computed in 10-May planting than 10-March due to excessive heat stress (>40 °C) during early phenophases while reduced variations observed in later phases. Reproductive stage initiation and accumulated higher thermal time delayed in late mature varieties compared to short one with lower root mean square error (RMSE) and higher coefficient of determination (R 2 ). Significant reduction in days after planting to attain maximum LAI, CGR, TDM and SCY-heat use efficiency (HUESCY) decreased with delay in planting with good statistical indices. Less impact of cold shock and heat stress on 21-April and 10-May plantings noted while 10-March and 21-June planting had higher incidence during early growth phases. Cotton varieties MNH-886 and NIAB-9811 (NIAB-Kiran) planted 30-March to 10-May exhibited higher resilience to variable weather conditions with fostered growth potential and yield. Variety NIAB-112 seemed heat tolerant and it can be recommend for early and especially for late plating while MNH-886 and NIAB-Kiran can be adopted at farmer's field in the region for maximizing cotton production under variable environment.