Here is a solid Bluegrass style arrangement of there is a time that utilizes the Bum-Ditty rhythm for the picking pattern. Pay close attention to the picking pattern as marked in the tablature. There's also some great Bluegrass, Bluesy and Pentatonic licks available here.
The original recording of this tune is in Dm, and was also played in the key of Bm on the Andy Griffith show whenever "Charlene" would sing lead. This arrangement uses Am shapes, and with the help of a capo placed at the 5th fret we can play in the original Dm. If placed at the 2nd fret we'll be in Bm. There's lots of great bluegrass style lick vocabulary out of this shape and the fret hand chords for rhythm lay out nicely.