From site:
"Your work is recorded in shifts. When we create a new block you get a share of the income proportional to how much of the work in the last 10 completed shifts is yours."
Why is it good to have ~1h shifts?
Average block finding rate should be ~4h
Calculations:
Diff*2^32/hashrate/time in seconds
1418481395*2^32/420000000000000/3600 = ~4(h)
Now we are having ~20h run to get block and there has been way more than 10 shifts in it - some of our effort will be lost now. Maybe shifts should be 4h or smt like that?

Shifts were 40 minutes when I joined. You can view the complete shift history back to the beginning of bitminter. It's a constant amount of work, not a constant amount of time.
And the fact of the matter is that when we work together for a long time without finding a block, none of us get rewarded. It's as simple as that, and no tweaks to the rules can change it. When we don't find a block, work is "lost," period. Work doesn't automatically have value.