In my conlang, what I've been calling "default tense" describes something
completely different. It's the tense that is implied when a 'verb' is
dropped and replaced by an 'adverb' (these word classes are quite different
from English verbs and adverbs, and might (I'm not sure) better be described
as 'preverbs' and 'verbs', respectively). The implied tense is often
whatever tense was used last, though there are some complex rules that I
haven't completely worked out yet.