Turkish has specific suffixes to talk about time. For example, to express in the evening, in the morning or in the midday, the suffix -leyin is attached to parts of the day, resulting in the words akşamleyin, sabahleyin and öğleyin to express specific times of the day in the form of an adverb.
This suffix does not obey the rules of vowel harmony, so akşamlayın is not a word. Also, instead of constructing öğle-leyin, one of the le sounds drops to prevent repetition of the le sound, giving us öğleyin.
The genitive case suffix -İn is uniquely added to kış and yaz, giving kışın and yazın to express wintertime and summertime respectively, it does not work for ilkbahar or sonbahar. There is no other place where you use the genitive case suffix for expressing time. For example you cannot say haziranın*, çarşambanın* or akşamın* to talk about time.
Another common way to express habituality is to add the suffix -lErİ to days, parts of the day, or the word for month, ay. For example akşamları, çarşambaları and haziran ayları mean in the evenings, on Wednesdays and every June.
