My old heat pump packed in and a hew one was installed last week. Ever since i’ve noticed the oven clock is running fast, gaining up to an hour a day and lights have a constant flicker. We had moved out for a couple of weeks before the heat pump was replaced so can’t be sure the issue predated the new heat pump. Ive seen other threads saying that electrical frequency could be to blame for digital clock and lights, often related to mains electricity. Could the heat pump be causing this change in frequency!
The heat pump is unable to "change the frequency" of mains power since that is tightly and accurately controlled by the power utility.
What is likely going on here, assuming you identify that this problem occurs only when the heat pump is operating, is that noise is being introduced into your home's power and that is tricking the oven clock to display the wrong time.
It's quite possible that there is some installation issue with the heat pump and due to that it being very "noisy" electrically and causing this issue. Or it could be that the oven clock is just overly sensitive. Either way, a power line noise suppressor, which an electrician can install for you, may be able to help. Generally the closer to the noise source one of these can be installed, the more effective they are.