Yeah that's a good site - my teachers have used it quite a bit!
To be honest you don't need to really know about the history of the English Language for the synoptic unit (6) because it's about language debates so this won't be one of the topic areas (I'm assuming you're on AQA A though!).
If you meant to put unit 5, a brief history of the key dates is useful but you don't need to know loads of detail. Just know the date of first dictionary etc.
If you need more help just let me know and I'll try give you a few key dates if you think they will help!