I don't know if this means anything, but I noticed that when I used aluminium with a large surface area the reaction was fast, from under a minute for powder under the right conditions to 42min for aluminium turnings, and for these reactions I usually got between 800cm3 and 1000cm3 gas. However, I had three longer reactions which stood out:
1. Spray can (sanded to remove paint etc): 1h30min, 365cm3 H2 produced
2. Aluminium wire (diameter ~3mm): ~3 days, 370cm3 H2 produced
3. A piece of aluminium plate (thickness ~ 2mm): ~2.5days, 415cm3 H2 produced