Rob,
I don't know of a simple way to enforce a minimum length of an entered data point in Maximo. However, this can be done with a relatively straightforward automation script. Something like:
if not mbo.isNull("LOCATION") and len(mbo.getString("LOCATION")) < 6:
# Work Order Location Input does not meet minimum length requirement
service.error("custom", "WoLocMinInputLength")
You'll need to create a custom message in the MAXMESSAGES table (Database Configuration > More Actions > Messages) to give a proper message to the user when they enter a value that doesn't meet the length requirement.
You might also consider other conditions that may or may not apply to this rule, such as PMs vs on-demand work orders.
Hope this helps,
Alex