SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '568660fabe15723172300add990542bf878b573132260cb944b1d7125c0a2d16' 
  AND token = 'doC6gOiHXJxYNETbpw+2vTYDo25JX08fPtXHioXWWBk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00037

JSON explain

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