Not exactly sure if this is a bug or not, but it appears the missions for converting gold to silver, and silver to bronze fists full of dollas in strontium-90 are 1 time only. I see no reason why they should be this way since every other conversion mission lets me exchange indefinately.

They may of accidentally had the 7 day timers applied to them.

It is definately not 7 days. I have been waiting for these missions to pop a lot longer than 7 days, no joy.