I think there is no “best way” to enter or exit spread trades, there is only “your way”. Let me explain:
I personally prefer the open and the close to enter all my spreads. I don’t like to watch my spreads during the day and I focus only on the closing price.
Most buying and selling is at the open and at the close, especially in thin markets. When you use a limit order you can enter anytime you want (even over night), but you might have the problem of not getting filled. Limit orders are an important tool for getting in and out of markets with low volume.
If you are a trader from Australia, for example, you will find it very inconvenient to enter around the close because this would mean you would have to stay up all night, or you would have to give the responsibility to your broker. If entering at the close is not comfortable for you, just enter the next day around the open (I recommend to wait a few minutes at the open till the market slows down).
In the long run it doesn’t matter. It is more important that you feel comfortable with the timing of your entry and exit.