Many sentences built around predicatives have elements that correspond to Nominative subjects in English, but which are not Nominative subjects in Russian.
For example, the Nominative we in 'We don't have any caviar' corresponds to a prepositional phrase in У нђс нљт икрІ. Similarly, the Nominative I in 'I am cold' corresponds to the Dative in Мнљ хћлодно.
In this sentence type, the past and future tense are expressed by the past and future forms of бІть. Since there is no Nominative subject in the sentence, the neuter singular forms are used: бІло, бџдет.
ИкрІ нљт. There is no caviar.
ИкрІ нљ было. There was no caviar.
ИкрІ не бџдет. There will be no caviar.
У нђс нљт икрІ. We don't have any caviar.
У нђс нљ было икрІ. We didn't have any caviar.
У нђс не бџдет икрІ. We won't have any caviar.
Пћздно. It's late.
Хћлодно. It's cold.
БІло хћлодно. It was cold.
Бџдет хћлодно. It will be cold.
Мнљ хћлодно. I'm cold.
Мнљ бІло хћлодно. I was cold.
Мнљ бџдет хћлодно. I will be cold.
Нђдо дљлать упражнљния. [We/You...] have to do exercises.
Нђдо бІло дљлать упражнљния. [We/You...] had to do exercises.
Нђдо бџдет дљлать упражнљния. [We/You...] will have to do exercises.
Здљсь нельзї курќть. [You] aren't allowed to smoke here.
Здљсь нельзї бІло курќть. [You] weren't allowed to smoke here.
Здљсь нельзї бџдет курќть. [You] won't be allowed to smoke here.
Їсно, что у негћ большћй талђнт. It is clear that he has a lot of talent.
Їсно бІло, что у негћ большћй талђнт. It was clear that he has a lot of talent.
Їсно бџдет, что у негћ большћй талђнт. It will be clear that he has a lot of talent.