ee.Date.advance

// Defines a base date/time for the following examples.
var BASE_DATE = ee.Date('2020-7-1T13:00', 'UTC');
print(BASE_DATE, 'The base date/time');

// Demonstrates basic usage.
print(BASE_DATE.advance(1, 'week'), '+1 week');
print(BASE_DATE.advance(2, 'years'), '+2 years');

// Demonstrates that negative delta moves back in time.
print(BASE_DATE.advance(-1, 'second'), '-1 second');

# Defines a base date/time for the following examples.
BASE_DATE = ee.Date('2020-01-01T00:00', 'UTC')
display('The base date/time', BASE_DATE)

# Demonstrates basic usage.
display('+1 week', BASE_DATE.advance(1, 'week'))
display('+2 years', BASE_DATE.advance(2, 'years'))

# Demonstrates that negative delta moves back in time.
display('-1 second', BASE_DATE.advance(-1, 'second'))