No one knows how long Shisui had to wait or how many times he could use his MS jutsu KotoAmatsukami in succession.
He had two eyes that could both use the jutsu though.
Shisui apparently used it during his situation with AO & Yagura perhaps, and I doubt that was 10 years between that and the time he was gonna use it against Fugaku , before the massacre.
He could probably use it more frequently , but Itachi apparently had a Kotoamatsukami that had to wait a decade to recharge as well. That's what he told Killer Bee anyway. However, maybe he told Killer Bee that because Killer Bee wasn't a Leaf shinobi and he didn't want him to know Leaf secrets, just in case.
Or maybe, since, Sharingan lineage come from the Juubi and Kurama is apart of the juubi, when Itachi placed it inside Naruto, Kurama's chakra bonded with the Mangekyo sharingan recharge time.
The eye contact requirement or not.. Danzo had white bandages on and Mifune's eyes were visible. Danzo might've hidden his sharingan, but sharingan can see chakra (sasuke saw deidara's chakra underground) Danzo might've seen through the bandages & at Mifune's chakra (if MIfune has chakra) even though he wasn't activating any jutsu.
Since it allows you to enter the mind of the other person (in a sense) maybe it requires "head" contact. lol Or maybe the target doesn't have to look into your eyes, but you have to look into their's.