In addition, from January 2019, a gradual increase in the time between the blocks in the Ethereum network will begin. According to estimates of the developers, by April 2019 it will be 30 seconds (twice as long as at the moment). In addition to reducing the reward for the blocks, halving their number per unit of time will further reduce the profit of the miners using the PoW algorithm.
No this won't be an issue because most likely the postponed fork won't be until April 2019, most likely they will roll the update to next month February or maybe March 2019 as the latest.
The block times were a big issue in Nov 2017 because it took a while for the Byzantium fork to be rolled out, it took a while and lead to extremely long block times.
In the end the ETH dev team decided to reduce the issuance to 3 ETH per block instead of the original 5 ETH and make the block times back to normal (15 secs) for another 1.5 year or so. Most miners were happy because their profits increase slightly and it reduced the network congestion which was massive at the time.
