Re the BT check, I would expect it was an electrical check, but I don't know. It doesn't matter, as (to me) it means an engineer visit to your place wouldn't be needed, just perhaps to the exchange.
In which case a Sky line will be the same, as all they do is order the line from BT Openreach, with the LLU connection. That will certainly require the engineer to go to the exchange. The Sky checker will just be issuing a standard "cover all cases" staement about an engineer visit, as they can have no idea what the situation is re the line if it is disconnected at the moment.
Regarding the timescale, sorry I have no idea. All Sky can do is submit their order to Openreach and wait for them to schedule the job(s).
Every day you wait though is at least one day later for the installation.
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