Time planning for the accurate estimation of construction duration is important to prevent construction delays and successfully complete projects on time. Although the main reasons for construction delays differ among developing countries, several factors related to project characteristics and clients contribute. In this study, interviews and observations were conducted with TOKI (Toplu Konut Idaresi-Housing Development Administration of the Republic of Turkey), a major housing construction authority in Turkey, to explore construction delays. It was revealed that TOKI uses three factors to estimate total construction duration, which are the number of flats, type of drawings utilized during the tender stage, and nonworking days. Data analysis of the TOKI Projects Status Table, which lists detailed project information for 2800 completed TOKI projects, showed that most delays occurred in housing projects. Therefore, the construction delays for TOKI housing projects were investigated in this case study. The findings revealed that there is a wide construction duration gap between calculated construction durations using TOKI’s calculation method and durations indicated in official construction contracts between TOKI as a client and the awarded contractors. Therefore, it was emphasized that TOKI significantly shortened the contract duration, which ultimately resulted in delays for a considerable number of housing projects. These findings can be helpful for clients and project managers worldwide to mitigate construction delays. To effectively overcome construction delays in developing countries, suggestions are made for the need to develop accurate construction duration estimation models.