yeah its probably overthinking.. as so many topics in this sports like nutrition, training, timing etc.It's not, my wife takes it and she only does HGH and she improved her physique while on it and she is not an amateur lifter. So relax and enjoy your Metformin the benefit are well above the negligible probably not even real mtor side effect
at the end, get your protein and carbs in, be in a surplus, train hard and one will grow. But i guess we all think like crazy about food timing, meal frequency, training split, etc. etc. All things that probably change less than 1% in the big picture