It is safe to leave a portable generator unattended whether running or not as long as it's away from anything combustible and you have secured it such as by locking it.
You can leave a generator running when not home as long as it's secure, not around anything flammable and it has enough fuel to run then you can safely leave the generator running even when not home.
Portable generators can run continuously for up to around 21 days or 500 hours.
After that or even before then it's best to shut it down for awhile and then check the oil and if needed change the oil.
Other than that the portable generator can run continuously for a long time without any issues.
You can let a portable generator run 24 hours a day 7 days a week for up to about 21 days before you should shut it down to let it rest and check the oil and possibly change the oil.
As long as you have enough gasoline or fuel for the portable generator it can run for a long time.
A generator can run 24 hours a day as long as it has enough fuel and enough oil.
Portable and standby generators can be ran 24 hours a day but they should be given a break after 21 days if ran that long so you can check the oil and possibly change the oil.
But there's no harm in running a generator all the time 24 hours a day if you want too or need too.
When breaking a new generator in you should run the new generator for at least 3 hours to break it in and put a load on it as well.
You should also ideally start your generator up and put a load on it for a few hours at least a few times per month to ensure the generator is working and to keep fresh fuel running through the carburetor.
The amount of fuel a generator uses in an hour is around 1/2 gallon to 1 gallon of fuel per hour for larger generators.
Smaller generators including the 2 stroke generators usually use around 1 gallon in 5 hours which is much better but they can only handle small loads.
I have a small 2 stroke generator that provides about 800 watts of electricity and I can run that generator for around 5 hours on 1 gallon of gasoline.
So if I ran it for 24 hours it would use around 5 gallons of gasoline which is not bad.
A generator will usually run about 8 hours to 10 hours on 5 gallons of gas for larger generators.
Smaller generators can usually go 5 hours on a gallon of gas which means it will use around 5 gallons of gas in 24 to 25 hours.
The larger the generator the more fuel it's gonna use and the more load you put on the generator the more gasoline it's gonna use.
Adding gas to a generator while it's running is not recommended although it can be done safely.
The reason why you're not supposed to add gas to a generator while it's running is because you could spill some gas on the hot engine, hot exhaust etc and cause a fire or explosion.
I have however added gas to my generator while it was running for a long time and never had any issue.
I just make sure to pour the gas in slowly and be careful about it.
During a wind storm that took out the power for a week I had a generator running all the time to have electricity and about every 3 hours I would go out and top off the gasoline tank to keep it running.
Never once did I shut the generator down to refuel and it kept running all that time until the power came back on and I shut it off and checked the oil which was also fine.
If you're not sure if you can go without spilling gasoline then it's best to shut the generator off for a few minutes or so and allow it to cool down while you add some fuel.
Although generators can run for a long time it's okay to give it a break once in awhile and it will save you money on gasoline if you don't need it running constantly.
If you don't have enough fuel then you should only run it as much as you need too.
But if you have enough fuel then you can run it all day and all night if you need to or want too.