If so, there is no advance requirements! If there is a seat or room on the train, it's your seat or room! (Unlike most airlines, there are no capacity controls to AGR rewards! ) If fact, on my award trip in October, I got the VERY LAST room ON 2 TRAINS (out of 4) on my westbound trip!
If you're referring to transferring Continental OnePass miles to AGR points, as long as you call OnePasss by Fridaym the AGR points will post by the following Monday mst times.
For simply non-connection rewards, you can do it at amtrak.com. If there are connections, or sleeprs, you need to call the AGR rep to book the trip. You tell them the destinations, and they see the exact same options that you do if you plugged them into amtrak.com.
THen the tickets are instantly in the system, and you can print them out at your local station, or have them mailed to you.