今 would make this "what time is it right now?" So ima(今) can be omitted in this instance.
Nani ji desu ka literally translates to what hour(interpreted as time) is it? And the i is Nani is silent that's why it sounds like nan ji desu ka
That is a common assumption. Unfortunately it is incorrect. Simply asking 何時ですか？(なんじですか）, Japanese speakers would wonder what time you were talking about. 今、何時ですか is a set expression, meaning 'What time is it (now)?' and shouldn't be tinkered with.