For me the connection is doable but very tight if the inbound flight is behind schedule but I don't see a flight on GOL at 9-30am. I only see flights on GOL at 7-30am and 2-30pm so why not take a GRU-GIG flight on TAM, one of which leaves at 10-54am?
Wrt the return the 6 pm should be fine but I can't believe anyone would leave Rio on NYE when they could wait an extra day and experience Reveillon there.