def shifttime(self, timeshift):
		"""
		Hard-shifts your spline along the time axis.
		By "hard-shift", I mean that unlike for a lightcurve, the spline will not know that it was shifted !
		It's up to you to be sure that you want to move it.
		We shift both the datapoints and the knots.
		"""

		self.t += timeshift
		self.datapoints.jds += timeshift