Luno to luno you can send to email addresses, should be instant and no fees(ie, send from mates luno to your luno email address, its not going through blockchain, its just being transfered from one luno address to another.)
Exchange to exchange, convert to whatever altcoin both support and use that. DGB is almost instant, thats my choice, but say to luno, you'll have to use ETH as they don't support anything else.(ie, convert your btc to eth on whatever exhange you're using, send the eth to luno, convert the eth back to btc, make sense?)
Exhange to wallet for hodl, well, unless you need to use it from your wallet instantly, then delay doesn't matter
Wallet to exchange, yeah, you'll have to wait