4 hour forecast -> N hour forecast

[braddf]

No description provided.

[dantravers]

I think this is a very similar issue to: #499.
Both have uses.
Being about to turn the 4-hour forecast into a 2 hour for instance is useful for some clients, and RUVNL have this (actually they have 1.75 hours as a focus)
Adani Green would use a 2 hour forecast also.
The 9am forecast usefulu for RUVNL also for their day-ahead.
We need to think abot about if this gives people what they want before jumping in. It could scope creep quite easily I think. E.g. if you could display error metrics as the user wants them, as % errors, that's valuable, but probably a separate issue.

[peterdudfield]

Use 1,2,4 and maybe an option if they want to type it in