Just opened dbs vickers in which there are 5 free trades (or zero commission) till 31 july. Can anyone share similar experiences?

I can't advice on timing - but if I were you I would trade objectively (do it only if I have an idea with or without the deal) and not for the sake of using up the promotion

Really good timings to enter rarely come by, it all goes down to your investing horizon, if your intended investing horizon is longer than 10 years then it would not make much differences in the overall outcome as long as you enter at a green price and not in times of reversal/market downturn.