What would be a good time for a 10k run for an individual that has been training for 3 weeks?

I've been an avid road/mountain biker for about 5 years now and haven't really ran all that much. I'm 24 years old, 5'10", 186lbs. Here recently (3 weeks ago) I decided I was going to start training for a Half Ironman. The event is not until July, however today I ran my first 10k, completed it in 54:54 with a 9.01 min/mile. Is this decent for someone who has never ran more than 2 miles just 3 weeks ago? There is a HUGE difference between biking and running, def felt it in my shins! I'm hoping by July 9th to get down to around a 6:30 min/mile. What do you think?