Calendar spreads are an interesting strategy in the stock options world. Before we dive into them, do you know what they are? A "time" calendar spread is usually placed during low volatility times, hoping for the stock to rise in volatility. Usually you sell either a call or put ATM, about 30 days out from expiration. Then you also buy a further ATM stock option. Whether buying puts or calls, you have to make sure the strike price you decide to sell and decide to buy have the same strike price.
In order to possibly profit on a double calendar spread trade, the trader would need to buy each spread at least a minimum of 30 days before the earnings are released if not earlier. You want volatility to go up, basically rise as an earnings event is coming up.
The trader wants to be out of the trader before earnings release. Make sure and keep tabs on when this is being released. Waiting until earnings is released while having this trade is a no-go! This will potentially eat into your profits and be a waste of a trade.

Put credit spread strategy built in 2018. I opened this credit spread on 8/17, and saw the profit materialize quickly. The stock was doing exactly what the market was doing, going up! The premium taken in for making this trade was about 70 cents, that's a great price.$0.70 Luckily, AFTER I closed my position, amazon hit its top for the year and slid down.