Regarding theta value

Will the theta value be deducted from premium on market hollyday i.e Saturday and Sunday?

Deductions don’t happen when when markets are closed, it all gets priced in automatically when markets are open.

Yes you should count Saturday Sunday while computing theta value.

Theoretically speaking if you are buying a nifty call with rs5 theta per day on Thursday and you are holding it for 5 days than probably price of call will come down by 30 rs by Tuesday if index remain at same level and there is no change in implied volatility