SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51f605b748070bb6d98c4dcde9cafe52f8f8eb6a5970c200f9a843425d079810' 
  AND token = 'gixIAOx3rk+ccC4IDHIJd8jvxOyk0RFYJHAnXR4uOlU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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