its usually fairly easy to tell when there are multiple hours left in a block.
is it?
If you take the assumption that since 3hours have passed then it will end soon. soon as in 3 hours later or in the case last week 8 hours later.... SARCASM.
You have to get lucky and you will most likely lose more BTC than gain. unless you are doing 20gh/s+ then it doesnt much even matter just misdirected greed