The rising edge of the switched live turns the light and the timer supply on
When the switched live falls the timer starts counting and as it does it supplies the fan from the permanent live unit it counts to zero
What happens if the switched live is half way will vary by product
Once it goes wrong you'll know.
The problem is that the manufacturer has tested a board full of their own devices under every possible temperature, load and abuse. If there's a failure in proper use you can reasonably blame them.
If you put 'something that fits' in (maybe like you...
Two things
Not used that one but on smaller models I remember the interface (PC or LCD) was a bit clunky and for instance you couldn't raise a LV disconnect above a LV warning
BUT
The trouble with LV disconnects is that the on load voltage for AGM can seem really low while still technically...
See if you can safely wire them up to see if the light output is what you need and how the light 'washes' the walls near the ceiling edges
Remember that fitting locations may be determined by the ceiling contents/structure as well as your taste
Or these days:
The designer, J Smith Esq ltd, long retired, who once did an outline drawing subsequently used in 10,000+ installations
The installer, who subbed it to a kitchen fitter he knew from a weekend demolition job
The inspector (of remittances) who works in the accounts dept of the...
Before getting excited check the spec on the virgin box. A lot of the 'Fibre to analogue telephone outputs /converters are only good for 2 basic telephones at a time (more if cordless /electronic)
A history of overheating or blown main fuses would be unsatisfactory. All-Electric House with 2 showers, massive ovens/hob and an EV charger on a 60A fuse maybe also so . .
Otherwise you are
a) Guessing
b) Making unsafe assumptions that Breaker Ratings somehow reflect maximum demand rather...