Hi Marc,
BO Cloud doesn't seem to have a YTD, MTD components like you would with Design Studio. However, I found the following two options really helpful to achieve what you're looking for.
The quick and dirty:
Create a time-series chart. The chart has a prebuilt YTD filter, as well as other nice filters as you can see below.
Otherwise, you can use input control (filters) in the following manner. Still does the job.
Final look:
As you see in the final picture. I am technically showing YTD. The user has to change "May" to "June" when June's data come in.
I hope this help!