class_docstr: Calculates the time elapsed since the first datetime (in seconds).
  
  Description:
      Given a list of datetimes, calculate the
      time elapsed since the first datetime (in
      seconds). Uses the instance's cutoff time.
  
  Args:
      unit (str): Defines the unit of time to count from.
          Defaults to seconds. Acceptable values:
          years, months, days, hours, minutes, seconds, milliseconds, nanoseconds
  
  Examples:
      >>> from datetime import datetime
      >>> time_since_first = TimeSinceFirst()
      >>> cutoff_time = datetime(2010, 1, 1, 12, 0, 0)
      >>> times = [datetime(2010, 1, 1, 11, 45, 0),
      ...          datetime(2010, 1, 1, 11, 55, 15),
      ...          datetime(2010, 1, 1, 11, 57, 30)]
      >>> time_since_first(times, time=cutoff_time)
      900.0
  
      >>> from datetime import datetime
      >>> time_since_first = TimeSinceFirst(unit = "minutes")
      >>> cutoff_time = datetime(2010, 1, 1, 12, 0, 0)
      >>> times = [datetime(2010, 1, 1, 11, 45, 0),
      ...          datetime(2010, 1, 1, 11, 55, 15),
      ...          datetime(2010, 1, 1, 11, 57, 30)]
      >>> time_since_first(times, time=cutoff_time)
      15.0
code: def __init__(self, unit="seconds"):
      self.unit = unit.lower()
  
file_path: featuretools/featuretools/primitives/standard/aggregation/time_since_first.py
imports: from woodwork.column_schema import ColumnSchema
  from woodwork.logical_types import Datetime, Double
  from featuretools.primitives.base.aggregation_primitive_base import AggregationPrimitive
  from featuretools.utils import convert_time_units
  from featuretools.utils.gen_utils import Library
label_desc: Use image node_id 1 to create a new TimeSinceFirst object from inherited base classes: AggregationPrimitive with example: obj = TimeSinceFirst(unit)