I can't think of an obvious meaning or context. I did a Google search and the only place I saw it was on Alibaba.com The search results showed blankets for beds. Can you give us the context?

It is referring to a given "time frame." For example, I can say to my boss, " Can you give me a blanket period for the presentation on Friday?" And he could answer saying, "Sure. Can you have it ready by next week then?" I hope that helps

If we compare the phrase with blanket bombing: it means when you have a large amount of time.