int <- interval(ymd("2001-01-01"), ymd("2002-01-01"))
# 2001-01-01 UTC--2002-01-01 UTC
int_shift(int, duration(days = 11))
# 2001-01-12 UTC--2002-01-12 UTC
int_shift(int, duration(hours = -1))
# 2000-12-31 23:00:00 UTC--2001-12-31 23:00:00 UTC
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