You need to allow some extra time at that time of day, because the buses leaving DTD will be stopping at Pleasure Island & Typhoon Lagoon on the way out, and Typhoon Lagoon traffic may be congested if a lot of guests are exiting.
You can take a bus from DTD to Fort Wilderness, and when you arrive at FW you'll need to transfer to the internal shuttle for another 10-minute ride to Pioneer Hall. The shuttles run every 5-10 minutes.
Or, you can take the bus from DTD to Wilderness Lodge and transfer to the FW bus, which goes directly to Pioneer Hall. FW to Pioneer Hall is a 5-minute ride, but the bus runs about every 10-15 minutes.
Total time: up to 20 minute wait time for the bus from DTD, allow 30 minutes from DTD to FW or 35 to WL, then 20 minutes to get to Pioneer Hall. So up to 75 minutes travel time; leave at least 1:30 before show time.
An alternate route is a 10-minute walk from DTD to Saratoga Springs, where you can catch a bus to the MK, and from there ride the boat to FW.
10 minutes for the walk, up to 20 minute wait, 15 minutes by bus, up to 20 minute wait for boat, I'm not sure about the boat ride but it's probably about 10 minutes. So total time is about the same.
I'm sure someone will come along and suggest a taxi to FW. That will save you time, but you'll still have to take the internal shuttle bus to Pioneer Hall, so factor in that 20 minutes. Probably 1 hour before show time would be safe, or you could cut it close at 50 minutes.
It will still be light at that time, so if you arrive early you can walk around, look at the horses, browse the gift shop, etc.