  Millisecond magnetars are often invoked as the central engine of some
gamma-ray bursts (GRBs), specifically the ones showing a plateau phase. We
argue that an apparent plateau phase may not be realized if the magnetic field
of the nascent magnetar is in a transient rapid decay stage. Some GRBs that
lack a clear plateau phase may also be hosting millisecond magnetars. We
present an approximate analytical solution of the coupled set of equations
describing the evolution of the angular velocity and the inclination angle
between rotation and magnetic axis of a neutron star in the presence of a
co-rotating plasma. We also show how the solution can be generalized to the
case of evolving magnetic fields. We determine the evolution of the spin
period, inclination angle, magnetic dipole moment and braking index of six
putative magnetars associated with GRB 091018, GRB 070318, GRB 080430, GRB
090618, GRB 110715A, GRB 140206A through fitting, via Bayesian analysis, the
X-ray afterglow light curves by using our recent model [\c{S}a\c{s}maz Mu\c{s}
et al. 2019]. We find that within the first day following the formation of the
millisecond magnetar, the inclination angle aligns rapidly, the magnetic dipole
field may decay by a few times and the braking index varies by an order of
magnitude.
