Update basic-operations.md

Author: jangdan

docs/use-cases/time-series/02_basic-operations.md

@@ -216,7 +216,7 @@ ORDER BY hour ASC WITH FILL STEP toIntervalHour(1);
 
 ## Rolling time windows {#time-series-rolling-time-windows}
 
-Sometimes, we don't want to deal with the start of intervals (like the start of the day or an hour) but window intervals. 
+Sometimes, we don't want to deal with the start of intervals (like the start of a day or an hour) but window intervals. 
 Let's say we want to understand the total hits for a window, not based on days but on a 24-hour period offset from 6 pm. 
 
 We can use the [`date_diff()`](/docs/sql-reference/functions/date-time-functions#timeDiff) function to calculate the difference between a reference time and each record's time.