When using tsset or xtset, there are a bunch of frequencies that are standard and can be set easily
- help xtset -
daily, weekly, monthly, quarterly, halfyearly, yearly

I have a dataset in which there are time periods in years, but observations are available every 5 years...in every year ending in 2 and 7, e.g. 2002, 2007, 2012, 2017, etc
How do I set the period?
Code:
xtset panelvar year, delta(5 years)
Also, do I need to get rid of the rows without the observations, or is it irrelevant?