Unfortunately, I can't assure an estimated time. It really depends on development time.
You have some workarounds, tough.
The safer way is to use a fixed exchange rate.
There if a workaround if you may use the Fixer.io model exchange, but it implies modifying a PHP file. If you feel confident doing it, please, perform a full backup of your site before making any changes. Then, go to Plugins > Edit Plugins. Select the WooCommerce Multilingual plugin and browse to classes/multi-currency/exchange-rate-services/class-wcml-exchange-rates-fixerio.php
In line 11, change the first “%s” by your API Key. So for example, if your API key is _ADD_YOUR_KEY_, you should end up with a line of code like this:
private $api_url = '<em><u>hidden link</u></em>';
Save plugin changes and try it.
At the moment, there is no workaround for the Currencylayer model, so I’m afraid I can’t provide a workaround for that service.
In any case, I will personally inform you when there is a new version which solves the problem.