SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '76d157b75d3291de800cea246374260448342bf2c8792e73460d1c3170eaaeca' 
  AND token = 'XfCg+pl1hsb2qtjWgoLsS4lIUMr1toDXmifAwEqAPWM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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