SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '74321bfe7d7ff3914520a25f8ec840a5dcbf4d32861d9d962fab4a475878f707' 
  AND token = 'JbbMpuiCjKhbvDEEZahVUWOfOiLKIwDo/EIgjlMDNoc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00030

JSON explain

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