How crucial is visa application timing?

[Splinter1]

I'm a British citizen living with my Argentine partner in Argentina and prior to starting the spouse UK visa application, I'd like to know how the timing of all this works.
When she makes the application and let's say it takes three months, should we already have a leaving/arrival date in mind?
In other words, once approved, is a date already given?
I'm sorry for the dumb question but I haven't been able to find out on the UK government website about how the timing of visas actually works.
Thanks for the help.

[seagul]

I'm a British citizen living with my Argentine partner in Argentina and prior to starting the spouse UK visa application, I'd like to know how the timing of all this works.
When she makes the application and let's say it takes three months, should we already have a leaving/arrival date in mind?
In other words, once approved, is a date already given?
I'm sorry for the dumb question but I haven't been able to find out on the UK government website about how the timing of visas actually works.
Thanks for the help.

For many applications especially from outside the UK there are a lot of checks are being made which means that these can't be processed until the intended of travel. Also once its granted then the applicant only have 30 days to travel.