SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '68fe8cb73712e84bb524f408c964a968a38a937a36b02a34cd9f25f62d1de508' 
  AND token = 'flgKY+eMqwc+j3J7mtQPtZJjjNWHeX3ksgTAHkAw2+o=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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