@SureTrader, I have experience of trading double cals on the SPX - I did a lot of them in March and April when the VIX was very high and they were good. However, after that I consistently started losing money on them as the implied vol fell but the SPX was still moving a lot, meaning I was getting hurt by the gamma. It's great to see that you have produced a very good return from them.
In terms of entry, the key thing is not what time of the day, or the day of the week to enter - I found it was more a case of with the vol difference between the short and the longs. So, if the front week shorts have a very high vol, and the back week longs have a lower vol, then that is the ideal time to enter. Double cals actually have quite a complex vega/gamma/theta dynamic I found (well complex for my little brain). There are many moving parts, and oddly enough theta being the least important of the 3 greeks. Sometimes, I found that the price of the dbl cal would drop even though the underlying index hadn't moved at all, and this was because of the subtle shifts in the volatilites. Many times, I found that the SPX would shoot past my strikes, and the cals would fall rapidly in value. Also, a lot depends on how many DTE's you have to your shorts. the less DTE's, the more sensitive the dbl cal is to all the greeks. I found dbl cals to be mainly a vega play.
If you are able to post an example of a trade, then that would be great.