In modern Mandarin, the correct way of saying a time (for e.g. 7:10 pm) is 七点十分 (qi1 dian3 shi2 fen1）. "fen1 分" means minutes.
But in colloquial Singaporean Mandarin, it's common to say (7:10pm) as 七点两个字 (qi1 dian3 liang3 ge4 zi4).
"Zi 字" here means 5 minutes. So two "Zi 字" means 10 minutes. Thus, 15 minutes will mean 三个字 (San1 ge4 Zi4 - 3 Zi). The use of "Ji Ge Zi 几个字" (how many zi) is quite common in colloqual Singaporean Mandarin.
My personal explanation is that alot of early chinese immigrants to Singapore were not used to the western timing system (esp. how many minutes) used by the British in Singapore, which used seconds and minutes. Instead, they only know the ancient chinese timing system, which used "Shi Zhen 时辰" system. The ancient chinese minutes system only have 12 "digits" or "zi 字" (corresponding to combination of tiangan dizhi 天干地支）. One "Zi 字" corresponds to 5 minutes.
Consequently, these 12 digits are the '12 Zi 字' as used in Singaporean Mandarin. These early chinese immigrants attempted to convert the western minute system into the chinese system and instead used 5 minutes as one unit of 'Zi 字' to count the time. [In case you might want to know, Bazi 八字 represents the birth date i.e. year, month, day, minutes of a person in chinese culture]
It was also easier in early times, as many chinese immigrants were illiterate. So how many "zi 字" makes timing easier.
Thus, it would seem Singaporean Mandarin still preserves alot of classical chinese annotation of timing. I'm not sure if my explanation is correct.
Does anyone know why Singaporean Mandarin say ""Ji Ge Zi 几个字" when referring to how many minutes (time) ?