could you please tell me if the 10 min train link between Beijing west and beijing central is open?

It is a bus, from Beijing west to Beijing station, you can also take Bus No. Te 2 as well. The duration is about 30min.

what time do the busses start operating from Beijing central station? I have to get to Beijing west station by 6am...

For the bus, the first one if for 06:00am, maybe you need to take a taxi instead. I noticed that there is a underground rail link which might be the one you mentioned. But according to the internet, it is still under construction. May become available after March 20. You can check it later to see if there will be schedule in details.