Renewal suggestion

Dear members , can I get some suggestions about my stamp 4 renewal pls . My stamp 4 is expiring in the 1st week of January. But I'm travelling in the 1st week of December for a month. My approval letter says I can Renew in 2 weeks advance. Now my questions are
1. Can I renew in 2 months advance. ? As I need reentry and reentry takes 2-3 weeks to come if you're apply through post.
2. I heard that nowadays burgh quay office don't give the gnib card on same day , they send it by post. Is it true ?
3. What would be the best time to go for renew , I mean how long before my travel date.
Thanks in advance. Help will be much appreciated.