@martin There is some suggestion that tight hip flexors could exacerbate plantar fasciitis, it wouldn’t do any harm to stretch them too in case that helps?
The stretching exercises I was given by physio were to stretch the calf muscles and tendons to reduce over-tightness – this did help me but I have flat feet and collapsed arches from long ago (and heredity) so support essential and walking around in unsupportive footwear or with bare feet makes it worse for me.
The pain getting up out of bed I believe is the tearing of tissue that has “healed” while resting and these exercises help to stop the “healing” of overtight tissues so in my case at least it was OK to begin as early as possible, but the root of the treatment for me was the insoles.