At the moment we don't support multi-currency when using the time billing layout.
Please vote up if this is important for your/your client's business.
My business is 100% time-billing based, and I'm about to make the leap to AR 2019.4 Premier for multicurrency. I can probably fake it on Services layout in the short term but really do need this to be time-billing based.
ETA for this feature please. Xero at half your price can do it. In the UK FreeAgent for a tenth your price can do it.