how long does a dogs first heat cycle last

how long does a dogs first heat cycle last. There are any references about how long does a dogs first heat cycle last in here. you can look below.

AE AL AS AT BE BG BS BY CA CF CH CI CL BW ID IL IN JP MA NZ TH UK VE ZA AG AU BD BH BR BZ CO DO EC EG ET HK JM KH KW MT MX MY NG PE PE PK PR SA SG SV TR TW UA UY VN COM CZ DE DK DZ EE ES FI FM FM FR GR HN HR HU IE IS IT KG KZ LA LI LU LV MS NL NU PL PT RO RU SH SI SK SN TG TN TT