Time Crystals are available within the land expansion and on in the non-card market. See:
How to Purchase Time Crystals via Shop
Step 1: Navigate to Shop using the icon in the menu bar in-game. Next, click Land Items.
Step 2: Select Time Crystal. Next, input the amount of Time Crystals you wish to purchase. Input your payment method (DEC or DEC-B).
Step 3: Click Purchase and note your updated Time Crystal balance by navigating to Land.
How to Purchase Time Crystals via Land
Step 1: Navigate to Land using the icon in the menu bar:
Step 2: Click the green + icon next to the Time Crystals balance (pictured below):
Step 3: Input the amount of Time Crystals you wish to purchase and select your payment method (DEC or DEC-B):
Step 4: Click the Buy button.
Step 5: Review the quantity of Time Crystals you wish to purchase, and click Confirm if you would like to complete the purchase and sign the transaction. Click Cancel if you need to make adjustments.
Step 6: View your updated Time Crystal balance.
**Note: You may also purchase Time Crystals while building a Worksite.
Please check out the Time Crystal FAQ for any other questions.