Second and vteřina

It occurred to me that Czech vteřina (second, as in minutes, seconds and hours) is related to the ordinal second (which brings me to the question: why did they choose second over all other ordinal numbers to name a unit of time?). Second in Russian is второй (vtoroy). Even though second as a number is druhý in Czech, you still see that stem under disguise in úterý (Tuesday), related to Polish wtorek and Russian вторник.