SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '831e39d166858807fccbe0f8d725c3842532ba71927a1570686fc6eac1abe98c' 
  AND token = 'PQQleT3bc4ADGmh1s7WaD1uYEwBEvcO1HrCMLa9bHtk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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