Kale is cold hardy and so is spinach. I do start kale in pots mainly because I only need a couple of plants. I soak the spinach seeds overnight to speed germination and I direct sow.
Spinach can germinate in 45-65 degrees, so you should be able to sow soon.
Chard can be planted 2-3 weeks before the last frost date. For zone 7 Maryland that is April 15, so you should be good to start all of your seeds now. Chard is cut and come again so I only need a few plants so I sow the seeds in pots and transplant them out. Since chard can tolerate warmer conditions, succession plantings can be made to extend the harvest.