Wouldn't it be nice if we could glean all of the info we need about a hive from watching the entrance? Here is a book about that:
https://drive.google.com/file/d/0Bx7DrOGMiXtlV2MyNTJpN2NqeVk/view
Thanks to the previous poster for all those resources in one place! And for the posters before, sharing your perspective and approach.
I note the number of foragers returning in 10 sec (I raise a finger for every group of 5, while I count 10 sec). And I note the # returning with pollen (out of 10).
For a split, that is raising its own queen, watching the entrance has been a reliable indicator of the state of the hive - queenless or good! the enthusiasm with which they are foraging, and seeing around 4/10 or even 5/10 with pollen, is a very reliable indicator that their queen is doing well.
A large hive does not send clear signals. I can say that during swarm season, if you are counting returning foragers every day at the same time, you will see a drop in foragers the day after a swarm. But... even though a swarm leaves with something like half the bees, there are more bees just about to emerge, and many nurse bees just about to become foragers. So, in a week post departure, I don't see a big difference in the number of frames covered with bees for hives that swarmed vs hives that didn't. So I really try hard to check in swarm season in a timely way to detect that a hive swarmed - no more than 14 days between inspections. I really want to know if they swarmed, because I am only breeding from queens who do not swarm when given enough space.
And during the summer, I have watched pollen collecting very closely. In my area, once it gets hot, the bees collect pollen from about 8-9 AM and about 730-830 PM. But... a big hive apparently can collect more than they need, and then "skip a meal". I have seen large hives with as few as 2/10 foragers bringing in pollen, started to feel bummed that the queen is a dud - then found plenty of brood when I opened up. They just had enough pollen with 2/10 bringing it in. They also often had 15-20 foragers in 10 seconds too - so 90-120 a minute. That's the max possible, it seems, without dropping in lots of extra capped brood...
I aim to check production hives (with honey supers) about every 2-4 weeks, outside of swarm season. I don't want to lose steam with honey collecting, so I would want to know ASAP if they need a new queen due to a failed attempt at mating. And that's a black mark on their record, if they swarmed or superceded without successfully bringing in a mated queen - I want to work with hives that can start superceding in time to try again if she doesn't make it back. That trait appears to be heritable, can be selected for. So I'm selecting for it - but I have to know more about the state of the hive to know if the hive swarmed, is superceding, failed their one attempt to get a queen mated...
In a couple of years, I will trust my stock more, and I will have a couple of outyards that I am not using to select for breeder queens. So those ones will be once-a-month yards for sure.
But... I am able to quickly tell if a hive is OK based on a brief inspection, like after the 2nd frame or so. A well functioning queen results in a well-ordered hive. But that ability was gained by checking every 7-10 days for the couple years before. And if there is a problem, then I have to dig in more, and so I don't try to do "quick" inspections where I am relying on finishing a hive every 10 min. I would rather finish a hive as needed, as long as it takes - so I can't bet on not finding a problem!
So it all depends on your goals for beekeeping, on your willingness to accept that you might miss a chance to save a hive. I would not recommend only checking a hive seasonally - as in, once a season - for someone with only 1 hive, or as few as 2. That's an expensive mistake, to not realize a hive is light on stores until they starve, or that they were queenless mid summer...
I really don't like mystery losses, so I am motivated by fear to check more! That's not necessarily a positive...
Every inspection is a chance to lose a queen. I aim for that balance between getting necessary information (or lessons on a how a hive "works"), and leaving them bee...