Add this code to the functions.php in your theme folder, and it should show up again.
The reason it doesn’t show by default anymore is because the new opening hours format in 2.0 is set through dropdowns ( users who upgraded have the option to use both the textarea or dropdowns, new users only get the dropdowns ), and show them in a table instead of a ( possible ) single mon – fri 9-5 line. And since they are in a table they take up much more height in the info window.
When I added the phone, fax and email fields, together with the opening hours ( set through the dropdowns ) to the info window it was to high to fit on the map, which is a problem. So I decided to leave them out by default, but I forgot to mention this in the release notes, together with a link to code that could restore it for 1.x users who set the opening hours in the old format.
Entering the opening hours through the dropdowns makes the format more predictable, and allows me to in a future release add schema.org support ( this helps Google to understand the location is open on a Monday from 9-5 ) to the plugin.