adapt SLAs to Services in practice

[XFab]

Hello Community,

we are in Service Design at the moment and created a Service let it call Communication.
The Service Definition of Communication contains all Services to communicate, like e-mail, sharepoint, web and so on...
My issue now is, to adapt the values of SLA in our OTRS system.

How is it used in practice, actually?
Creating a Service called Communication -> Creating Sub Services for e-mail, sharepoint... -> add SLA called availability and complement the values for FRT, MTBI, etc.?

At this point with complementing the values... If I have my Service Catalouge, e.g. the availability is described in percent or also in hour/year. But how to configure it in OTRS now if the Mail-Service is allowed to be down for 5 hours in a year?
I hope somebody can help me.

Thanks