translation

I'm looking to translate "in their darkest hours/times" but have struggled in understanding the grammar required for this?

In Quenya, I'd offer:

• amalúna lúmeltassen
  ama-lūna lūme-lta-ssen
  "in their very dark hours"
  (Possibly amalúne, but most current late-period attestations point to singular adjectives with nouns in adverbial cases regardless of number.)

• mi amalúne lúmeltar
  mi ama-lūna-i lūme-lta-r
  "in their very dark hours"
  (Optional independent preposition.)

And in Sindarin (assuming dûr "dark" < *ndūrā):

• mi lui enduir dín
  mi-n lû(-ī) an-ndûr(-ī) tín
  "in their very dark hours"

• mi lui ronuir dín
  mi-n lû(-ī) ro-ndûr(-ī) tín
  "in their darkest hours"

Wait for some more opinions!

This is fantastic, thank you Röandil. It is Quenya I was after. Got a bit excited when I found this place and forgot to state which language. I have quite a lengthy script to compose so really grateful for any help.