I'd push for a Skype interview. For permanent research&teaching (ie standard) lecturer contracts, we always fly people over, whatever the cost. We would expect them to be available for this. And we pay their expeses, take them to dinner etc. If we want to appoint someone, we want them to accept the offer.
But for a short-term TF position, I don't think we would, even though we do pretty much gold standard for permanent posts.
So contact HR and say that the only reason you're not able to attend is the breastfeeding situation & you would hope that they'd make a reasonable adjustment in this instance.
As for an advertised interview date - well, all I can say is that IME, this is always notional. As I say upthread, I'm currently rearranging my diary for the possibility of a series of selection committee meetings: shortlisting then interviews & presentations. If the chair of the committee, usually a Dean, has other more pressing commitments (a meeting with the VC or a DVC) then my diary has to adjust to hers. And so on.
One thing - when does this TF start? And what arrangements will you make for childcare &BF then? When we have a TF post, it's always because we need someone now to cover essential teaching - neither we, nor the successful candidate, can have the luxury of negotiating a start date.
If I were you, I'd have a clear strategy & be prepared to mention it if asked. As much as I try to be a good feminist academic, a TF post where I need specific teaching covered, to an existing timetable, I'd have a concern about your situation. For me, it wouldn't affect my decision if you proved to be the best fit for the post after the recruitment exercise. But I would be concerned, and would raise it - rather awkwardly & reluctantly - in any post-offer conversation.
It would be different if it were a permanent lectureship: we regard those (at my place anyway) as long term commitments, and initial negotiations about start date and paid hours/teaching timetable restrictions etc are more flexible. For a TF, they are generally not flexible.