From the HPC gears website...

Approx. belt flank play backlash are as follows:
T5 - 0.6mm
T10 - 1.1mm
AT5 - 0.2mm
AT10 - 0.4mm
AT20 - 0.8mm

Wonder if I could turn a 5.08mm pitch pulley down a tadge. The 5mm tooth seems a pretty good fit in that.
24t * .08mm / Pi = 0.61mm off the diameter. Might work. Or am I completely getting the sum wrong?