SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '0121ee40fb9006005d9835e5977fd95c6783f2d36df07a9e368afc85b4634bec' 
  AND token = 'km/m1Ep/jbhRCIxsBLCSUwGc3aChPHhEPWmOJiYdLBQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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