Support for time domain waveforms
Bilby uses lalsimulation's XLALSimInspiralChooseFDWaveform() to obtain Fourier domain waveforms.
To add support for time domain waveforms I would recommend to call lalsimulation's XLALSimInspiralFD() to obtain Fourier domain waveforms from time domain waveforms implemented in lalsimulation. This has the advantage that lalsimulation is handling the conditioning and FFT.
Carefully read the documentation about the input parameters of this function! The redshift can be passed in the LALDict.