That's probably a question best answered by one of the professional drivers who mill round T5 waiting for their inbound clients, but until one comes along I'll give it a go:.
On a good day, when it all works, you can be off the aircraft and outside T5A with suitcase in less in 15-20 minutes. However 0600-0700 is the morning rush and timing will much depend on where their aircraft ends up parked - if they arrive at T5B or C they'll have fight their way onto the transit train to get to T5A and then there's the unknown wait at immigration. Any major delays there and the bags will beat them to the baggage belt. Personally if I wanted to play it reasonably safe and minimise my own parking/inconvenience I'd be pessimistic and plan on an hour.