In lojban, as in Chinese (I believe both Mandarin and Cantonese, although I'm not an expert), number is not implicit and is usually either irrelevant or determined by context. There are mechanisms for specifying number. Ditto tense. Things can be left even more fuzzy, or made more precise.
I think the easiest way to sum up Lojban is this (my understanding based solely on reading ABOUT Lojban, I don't know a single Lojban word... aside from Lojban):
Anything that can be said in any language can be said in Lojban. Anything that can be left unsaid in any language can be left unsaid in Lojban.
Thus while it is not possible to use the verb "to be" in English without expressing a tense, it is in some languages, therefore it is in Lojban. Presumably it is also possible to specifiy a tense when saying "to be" in Lojban. It can be done in English, therefore it can be done in Lojban.
In lojban, as in Chinese (I believe both Mandarin and Cantonese, although I'm not an expert), number is not implicit and is usually either irrelevant or determined by context. There are mechanisms for specifying number. Ditto tense. Things can be left even more fuzzy, or made more precise.