They are adverbs. Like other adverbs, they can be used along with any tense. It is the duty of verbs, not adverbs, to establish time frame. Even the adverb "retrospectively" which explicitly calls up the past can be used in any time frame: example: "A year from today I expect that I will feel retrospectively happy about what I am doing now."

Yes, these words can be used in any tense, but be aware that they have the effect of fixing the meaning of a tense by removing ambiguity. For example, I ate fish. (1. At a specific time in the past. E.g. For dinner last night. Or 2. As a practice in the past. E.g. Growing up in a coastal city.) I sometimes ate fish. (As a practice in the past. E.g. When I went out to restaurants) I would eat fish. (1. A practice in the past. Or 2. The result of a hypothetical. E.g. If I had a choice between chicken and fish) I would sometimes eat fish. (1. A practice in the past. = I sometimes ate fish.) Etc.

Yes they can!

Simple answer..YES!