So, as we can see, it all depends where you're flying.
In the UK, it's basically set 1013 when you're cleared to a flight level and QNH when you're cleared to an altitude. (Low Transition Altitudes in UK). This is the way most UK operators will act, no matter which country they're flying in.
In the USA, Japan (and it sounds like India); it's 29.92 going through TAlt and QNH when descending through TLvl. No dramas 'cos it's 18000 in the US and 14000 in Japan, so it's not likely you're going to bust a flight level.
In the UK, with low pressure, clearance to a low flight level and healthy aircraft climb performance, it is very simple to bust a flight level if you wait until TAlt to set 1013 and that is a very good reason for doing it as soon as you're cleared. Clearly in Yanky Land etc this isn't really a problem. The only snag I've ever got is trying to remember the damned thing and say 'thank you' to Boeing for giving me the ability to chuck 18000 or 14000 in the fix page. I know, silly old git
