Summer is a good time to order. They ship with cold or heat packs according to season, but when you reach deep winter, or even the stage when shipper and receiver may be in wholly different weather patterns, shipping gets far riskier. Just watch the weather map and talk to your shipper if you have to order in an iffy season. 'Weather smarts' help a lot, the ability to predict what your area will be doing.
Second caution: shipped fish will be in a bag you SHOULD NOT OPEN until you are absolutely ready for that particular fish. Read the sticky on DEATH IN BAGS and it will explain why. Rushing to open all the bags at once is a no-no. You have to be ready to acclimate, you need a refractometer, you need everything ready, and you MUST complete acclimation within 30 minutes. I hate like everything reading a post that begins: "I acclimated this fish for 2 hours and it's dead..." [There's a silent killer in a shipping bag once opened.] Read that sticky!