Setting the Bollinger Bands to a length of 30 days, we can see that there have been two times this year when we have been below 2 std dev. One between the 3-8 March. The other on the 12-13 of May. Both were followed by a rally to the basis.
I think the best time to go long will be somewhere at the end of this week: maybe on Thursday or Friday.
Also, if you are afraid of a possible crash I suggest you watch this video by Matthew R. Kratter on the matter: youtube.com/watch?v=42-hsgy-zuQ