Instructables
Picture of bike clock
CIMG0356.JPG
CIMG0352.JPG
just a little hinter for those wondering various ways to do this as i've seen a few but havn't had certain parts.

FINAL TAKE:!
complete - fully tensioned as you would a normal wheel
old 20" bmx wheel from halfords 36H, same spokes and nipples I used 12 of them 
44T sprocket off cheapo BMX
clock mechanism
Ive laced these radially so to match a clock

start with 2 opposite spokes - get them tight and even and the rest is easy, except knowing the exact time!
mechanism clamps on to center hole.

This can be done with most size wheels