I'm not sure what do you mean by "It takes time" to import them honestly since it only takes a few minutes . I would suggest keeping them on Paper wallets and simply re-type the private keys on Bitcoin Core when you want to sell them and then send them where you want to . (Coinbase or other services).
There is a lot of possibilities (after sending the funds to Bitcoin Core or other wallets - when you decide to sell) you can do one of the following :
1. Sending them to Bitcoin Debit cards : It's now possible to convert your bitcoins to USD , so you can send them to CoinsBank or E-coin.io and withdraw from ATMs and you are done .
2. Looking for someone to trade with : It may take some time (If you are looking to sell fast it's not recommended) since you have to find someone on the forums/LocalBitcoins with the payment method & fees that fit you .
3. Deposit to Neteller : You can deposit them to your Neteller account and then sell your Neteller funds using Card to Card method . (Note that Neteller won't allow you to use the funds to buy online or withdraw from ATM if you deposited using Bitcoin)
It actually takes hours though. He will have to import his private keys somewhere, then send to an exchange, then find the price. Sometimes bitcoin's price moves fast enough that you want to be able to move faster than that.
I would say that if you are considering selling soon, I would get a wallet like electrum set up and ready. Have your coinbase or other exchange account all set up too.
When you decide that you want to trade in the very near future, unfortunately you will have to store your coins at the exchange. That isn't a good long term strategy, you should have 2FA and a strong password. If the market moves against you, then get your coins back to your wallet.
just my opinion.