Is pollen from male viable/usable for pollination as soon as pollen sacks are visible?

No Mate you need to wait for them to begin swelling and opening up. Once they are at that stage you can either pollinate directly from the plant or collect some in something like a film canister for later. It's fairly important to keep moisture away from collected pollen as it will kill it's viability For long term storage I reccomend the freezer