I think most of us define each widget on a dashboard with its own individual period selections.
The fact that we can do this makes an over-all-style period selector a little unusual as a requirement, but I can see a case for it definitely.
Imagine a dashboard with a Summary chart on it showing how profitable a customer was in the past and then want to change the period to see how profitable they are in future periods. With other summaries showing the costs of materials were at the first time point, and the costs of labour over time, and how that would all work together with a period selector I am growing to like the idea even more.
Plus (In my opinion) it would be great to have another feature which makes Dashboards more interactive. I have spoken previously in other threads about the use of Variables being potentially useful in creating calculations. A way of adjusting a Variable like Time on a dashboard with a spinner or slider control would be really cool.
Anyway, back on topic! You could try making a dimension out of a date, but it would make the main database view look quite strange I think. Probably best to use a Cominationkey of YYYY-PP
2019-01 would be Jan this year
Then the years and periods would be in the right order at least.
Let us know how you get on