Bid ask spread movement is an interesting metric to track in a day. It has been observed in developed markets that it follows a U shaped pattern
More details in this paper :Limit orders and Bid-Ask Spread

In Indian markets case, came across a 3 pager in Economics and Political weekly that says that the bid ask spreads do follow the same U pattern.
Link : Are you getting a good deal?

It would be interesting to see how the option spreads behave amongst the NIFTY options in India !. Understanding Indian markets is anyways going to be interesting as it is an intense 9:55 AM - 3:30 PM game where all the instruments get traded.