Abstract Background: The application of appropriately timed herbicide is an affordable approach to optimize the activity of herbicides. Objective: The study aims to determine the best night-time to apply glufosinate, oxyfluorfen, and paraquat with emphasis on the role of the period of dark exposure after herbicide application. Methods: The study was conducted at two fields in Iran, the fresh weight: dry weight (FW/DW) ratio of five weed species treated with glufosinate, oxyfluorfen, and paraquat at 0.5x and 1x of labeled doses after sunset or before sunrise was assessed. Results: The application time-of-day effect for tested herbicides was affected by application dose of herbicide and was more pronounced when the herbicides were applied at the 0.5x as compared to at the 1x. In 14 out of 18 cases, foliage tissues were more desiccated with the sunset applications of herbicides at the 0.5x than with the sunrise applications. When applications were made after sunset, an increased foliage tissues desiccation of Chenopodium album L. treated with paraquat (29.6%) in field 1 and C. album treated with glufosinate (27.2%) or paraquat (23.7%), and Malva neglecta Wallr. treated with glufosinate (21.6%) or oxyfluorfen (31.6%) in field 2 was detected by increasing the dose from 0.5x to 1x. Except 4 out of 18 cases, the herbicides applied either at the 0.5x after sunset or at the 1x before sunrise resulted in similar FW/DW ratio in all weed species. Conclusions: If contact herbicides are used at night-time after sunset, it is possible to take advantage of their reduced doses.