Hi jackie. It's a bit difficult to be exact, it depends on how many carbs you are eating, how high your bm's are at the moment and your glucose intolerence. It will also be dependant on how much carb you reduce from your diet. But overall you should start to see some effect fairly quickly.
I assume that you are testing at the moment. Try keeping a log of what you eat, work out the carb content, and take reading at one and two hours after eating. This will start to show you what effect that meal has on your blood sugars, you can then try the same meal with some of the carbs removed. You should soon start to see the results.
When i first started reducing carbs, I set a target of 150g per day, This wasn't low enough so I reduced them further to 100g petr day. I reduced mine finally to around 20g per day. You will have to work to your meter , keep testing and testing and you will soon start to establish what works for you.
Hope this helps. I've tried to keep it as simple as possible to get you started, maybe you've already made some attempt at lowering your carbs.
Do you have any idea of how many carbs you eat at the moment, and do you test your bm's'
I've made a lot of assumptions in my reply, post a reply and gives us some more information, there's lots of people on the forum to give you help and advice