SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21ff38c1cc888829bccd312cbece19e943df874976135fdac554f344c3ad8ffe' 
  AND token = '/jz+FB8+CTuhPhCAZBSjyGw275vOPFJja5AR0G6+rcw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}