Citation for card index

Mbcross, your instincts are good. There are a few problems.

1. You feature the original card in your citation's Layer 1, but you don't have (or didn't give) enough data to do that. You say only what the card is, but you give the reader (and yourself at a later date, after your recollection of the record has gone cold) no idea where that original record can be found.
2. Your second layer, the source of the image, cites FamilySearch okay, but what happens if FamilySearch drops that collection after its contract with the provider expires? Your reader (and you) will have no idea where to find the actual card.
3. Your Layer 3, the "citing ...." layer states "Book 55, page 86" but that introduces another problem. We now have two "original" records with no statement as to where they are, the card and the book. What you have placed in Layer 3 is information from the card itself that cross-references yet another original document. The "Citing ..." layer (aka Location Layer) is where we report what the image provider identifies as their source. If we're citing a card index, or a birth certificate, or a loose deed with a notation that says "see Book X, page Y" that's part of the information that belongs in our abstract/transcript of the card, certificate, or loose document—that’s not data that tells readers (or us) where to find the item we’re citing.
4. Also, when we’re creating a reference note, we don’t put periods (full stops) between essential elements of the citation. In a reference note, those periods mean "end of citation to that source." Those full stops are used in a bibliography (source list) where the formatting is, by nature, radically different.  I think you know this already, judging from your past queries, but I’m pointing it out for newer researchers who will be reading our Q&A for years to come.

The fix for all this is simple.  Image 3 of that image group provides FS’s “citation” of where the original cards are maintained; so that's what we use in Layer 3.  Below, I've also tweaked your ID of the source so it uses the same exact label that FS uses (which is the only label we have to use), and I've eliminated a phrase at the highlighted spot because neither the record nor the image provider includes that information

     1.  Hill County, Texas, “Card index to Delayed Birth Certificates, 1869-1972,” Ruth Marie Harris, 25 August 1914; imaged, FamilySearch (https://www.familysearch.org/ark:/61903/3:1:3Q9M-C3S2-T31X-N : accessed 1 October 2024), image group number (IGN) 8507941 > image 865 of 5279; citing “Hill County Courthouse, Hillsboro.” 

If you want your citation to include a cross-reference to the original book and page, then you could do this:

     1.  Hill County, Texas,  “Card index to Delayed Birth Certificates, 1869-1972,” Ruth Marie Harris, 25 August 1914 (citing Book 55, page 86); imaged, FamilySearch (https://www.familysearch.org/ark:/61903/3:1:3Q9M-C3S2-T31X-N : accessed 1 October 2024), image group number (IGN) 8507941 > image 865 of 5279; citing “Hill County Courthouse, Hillsboro.” 

This approach serves two purposes: (1) it keeps together all the information from the content of the original card: name, date, and cross-reference; and (2) the reader now knows where to find the cross-referenced book—i.e., in the same locale as the card, for which Layer 3 reports the locale as given by FamilySearch.