1)
When did Avner go to Giv'on?
1.
Radak: This was after Avner took Ish Boshes to Machanayim, and before he made him king over Ashuri, Yizre'el, Efrayim and Binyamin on the return to his house. Giv'on is in Binyamin.
2.
Malbim: It was after Ish Boshes was king for two years.