That's hard to answer exactly and really depends on the initial mix of the character.
Ideally, a 6th level (3 ftr/3 wiz) could qualify for the class and be approved for a CDQ due to the BAB requirement of 4/arcane spell level requirement of 2nd level.
A straight wizard... they wouldn't qualify until much much later due to the BAB requirement stacked with the fact that you would need all of the armor feats (3) and the martial weapons feat.
If a straight human wizard took the following feats at the levels....
1st Armor Heavy, Armor Light
3rd Armor Medium
6th Martial Proficiency
They would be able to meet requirements at level 8 (if not human, level 9).
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