BTC transfer duration When BTC is mined, it is sent to the BTC wallet. The duration of the transaction can be up to 24h for online wallets.
 Is the duration faster, when transferring BTC to a “cold wallet”?
Coins are spendable by a wallet as soon as the transaction is included in a mined block. Some online wallets use their own software to sync, or in other words, to make their application aware that the account has received coins. Applications that use this method could have varying durations for recognizing received coins. Furthermore, different wallet providers may also have additional criteria, such as requiring that at least 4 blocks have been mined after the transaction was included in a block. This is known as Minimum Confirmations. For example, Coinbase will credit your account once there have been 3 network confirmations. In this case, the duration to "receive" coins on a local wallet such as Bitcoin Core, would be much faster than on Coinbase, because you would not have to wait for 3 blocks in order to spend the coins. It's also worth noting that this is not an issue of "online" versus "cold" wallets, it's more of an issue of third-party service based wallets versus personal wallet clients which you control the keys for.

As @JBaczuk pointed out below in the comments, technically coins are spendable even without a confirmation. This is especially useful for child-pays-for-parent (CPFP) transactions, where the first transaction may have a fee that is too low, but it is used as an input in a second transaction with an extra high fee, so miners will include the second transaction, which would also require including the first transaction.