SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '76bf749251b092395f536d094f13f44d4b949621297e182d5033fe81f150606a' 
  AND token = 'nX0FPN9agRlLDfPuTWcM4BGKGbDMcQmaEdHfEQgpb50=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00037

JSON explain

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