SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b52393b0a431ddec40cbdba62376d24f442c68a9da8bea8a56de30046f562f6d' 
  AND token = 'X0sMfDNUIYgSYmdpOBj3ldl+DYQnfbf/PIltU0/F3D4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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