You want a number. 4 hours, 5, the length of a working day. Then you can plan your week around it and stop feeling guilty at lunchtime.
There is no number that fits every dog, and using somebody else's number is how alone time goes wrong. There is a way to find your dog's, and you can start tonight.
The only limit that matters
The useful limit is the longest departure your dog gets through without starting to worry. Staying below that point is the condition for learning, in alone time as much as anywhere else.
For one 10 month old dog that is 4 hours asleep on the sofa. For another it is 3 minutes. Both are real, and the second one is not a badly raised dog.
Adolescence moves the figure around. Adolescent dogs are awake more and need more to do, and any skill goes soft without practice. A dog who managed a morning at 6 months old may not at 11 months old.
Find your dog's number tonight
Point a phone or a camera at the door and the bed, and leave for 20 minutes. Go out properly: keys, coat, car, the whole routine.
Watch the first 5 minutes closely. That is where the answer is.
Settled looks like: a wander, a drink, a look out of the window, then lying down within a few minutes and staying down.
Worried looks like: pacing, panting, drooling, whining, barking or howling on and on, scratching at the door or the window, and food left untouched.
Write down the time at which your dog settled, or the time at which the worrying started. That is your starting figure, not a verdict.
If the video looks like the worried version, stop the experiment and book a veterinary appointment before you train anything.
Practical limits worth keeping anyway
Even a dog who copes well has ordinary needs that set a ceiling. These are management rules rather than claims about behaviour.
A toilet break at least every 4 hours or so for most adolescent dogs, and sooner for a dog who has had accidents indoors.
Water available the whole time, and a comfortable temperature if it is a hot or a cold day.
Something to do at the start: a stuffed frozen toy or a chew given as you leave, taken away when you return.
A safe space rather than a big one. A crate only if your dog already likes it, never closed on a dog who is worried.
Nothing chewable and dangerous left in reach. A bored adolescent finds the cable, the sock or the bin.
A walk or a sniffing session before the long stretch rather than after it. A dog who has used their nose settles more easily.
Build the figure up slowly
Work at a length your dog is comfortable with, not the length you need. Start 2 minutes under whatever the camera showed.
Do 3 or 4 short departures on an evening rather than 1 long one. 3 minutes, 5, 3, 8.
Come back in without a greeting, and sit down. The return is as ordinary as the leaving.
Add time unevenly. A longer departure should be followed by a shorter one, so your dog cannot predict an escalation.
Keep filming once a week. It is the only way to know whether the extra hour is actually fine.
Behaviour change is built from management plus reinforcement together, and the management half is not leaving your dog longer than they can currently manage.
If you need longer than your dog can do
This is the common case, and it is a logistics problem rather than a training one. Arranging cover is inconvenient and is still the fastest route.
A midday walker or a neighbour who breaks a long day into 2 manageable halves.
A sitter in your house, which is usually easier on an adolescent dog than a busy daycare.
Daycare only if your dog genuinely enjoys it, and not as a way to solve worry about being alone.
Working from home on the harder days, and stacking the long days when cover exists.
Three things not to do
Do not leave your dog longer to prove they can cope. That rehearses the panic and makes the next departure harder.
Do not get a second dog to solve it. A dog worried about your absence is usually not comforted by a different dog.
Do not use a bark collar or an anti-bark device. A review of aversive methods found them associated with worse welfare outcomes and no training advantage, and punishing distress adds fear to it.
Relaxation is trained as a behaviour in its own right, in short repeatable sets below your dog's threshold. A dog who can settle while you are in the room has somewhere to start from when you leave it.
Safety note
Book a veterinary examination first if your dog cannot be left alone, or if being left has suddenly become difficult. Distress at being left is a recognised behavioural condition and a welfare problem rather than a phase. It does not usually improve on its own. Sudden behaviour change warrants a veterinary examination, and pain frequently presents as a change in behaviour rather than as obvious lameness. Then ask your veterinarian to refer you to a qualified behaviour professional who works with reward-based methods. Gradual departure practice, kept below the point where your dog begins to worry, is the core of separation-related behaviour work. A dog who is panicking should not be left at all while that work is set up. Get help now if your dog has injured themselves, broken teeth or nails, or damaged doors and windows trying to get out.
What to expect
A dog who is simply bored often shifts inside 2 weeks. That is once dinner comes out of a bowl and into a toy tied to your leaving. Genuine distress is measured in months, with help.
Nobody can promise you a dog who does a full working day. A camera, honest figures and a bit of cover are what get closest.
If alone time is one of several things going on at once, the Assessment will sort which to work on first. It is free, takes about 3 minutes, and asks for no email address.
Tonight's version, in one line: film 20 minutes, write down the minute your dog settled, and start 2 minutes under it tomorrow.