GD placed on Metformin 500mg XR

I have a quick question for all the Mommys. I am a FTm and was diagnosed with GD back in May and have been able to control my numbers through out the day but not so much my fasting numbers. I would wake up and test and they would be slightly high (i.e between 92-95). How long did it take for the medication to start working and your numbers come down. I took my first dose at bedtime last night and woke up to a fasting number of 99 which is higher than usual with the same bedtime snack that would give me low numbers. TIA & good luck to you lol