Octant

Colloquial spacer's term for a 50 day period (one-eighth of a star year). This has not replaced older terms such as the month (a 28-31 day period) or the week (a 7 day period) - though these old Earth periods have less significance on colony worlds with different year lengths.

The octants even have names:

Firstant : Day 1 - 50
Twotant : Day 51 - 100
Thretant : Day 101 - 150
Fortant : Day 151 - 200
Fivtant : Day 201 - 250
Sixtant : Day 251 - 300
Seventant : Day 301 - 350
Eightant : Day 351 - 400

So it is possible to talk of the '7th of Sixtant' meaning Day 257.