The date class is supported, just not for use as a real time clock on the remote. I asked for this when ProntoScript was released and due to lack of RTC hardware, Philips could not oblige.

The only thing you can do is to use GUI.getDisplayDate() or GUI.getDisplayTime() to get textual values that you can hopefully massage. As you cannot see Langage, TimeZone or DST settings from GUI, converting from String value may not be fortuitous.

However, if you are interested in only time deltas, new Date().valueOf() now is guaranteed to be a value of 20 higher than the same call 20 milliseconds ago.

This was discussed in a post by me around the time that ProntoScript was released. I believe you should be able to search for +new +Date +GUI +getDisplayTime and find the original post.