If you use the 60mah/4.8volt plug from the charger on a 6V/150mah pack, i'd guess the charge time would be about 3.5-4 hours.

An unregulated power supply that gives about 60mah at 4.8 volts would give less at 6V, say 50mah and since charging nicd packs is not 100% efficient, that's why I guess the 3.5 or more hours. At 3 hours or so just feel the pack. If its noticeably warm then its almost full.

Other than getting a better charger or doing a homebrew volt/amp meter harness to test power, this is probably the best you can do.

You can also try hooking up the 9.6V plug.. since its plugged into a 6V battery, you'd get MORE than 60 mah, maybe 100, then your charge time could be 1-2 hours ish?? hard to tell but use the warm battery test to be sure. and be careful with polarity if you try to wire up either connector!