Not my place to decide what the proper timing should be, as I'm not the dev, but my opinion is this:
skill timing should corelate with:
1. Agility (overall speed of character) - 30%
2. Stats associated with the skill used (i.e. Scavenging should take less time if you have high Charm/Perception, as you will find things faster than someone who has no perception whatsoever) - (20% primary, 10% secondary) - 30%
3. Weather conditions (try to gather sand in the rain or in winter irl @ frozen beach) - 40%
4. NOT skill level. Skill level should only affect the quality of the resulting material, not the speed of action. Stats are gained through practicing skill would affect the speed anyway, but if you lock the skill and loose the stats you will become slower.