Yes, you can use “by the time I get back to it” instead of “get around to it,” but there’s a slight difference in tone and meaning:
• “Get around to it” implies finally finding the time or motivation to do something after delaying or procrastinating.
• “Get back to it” suggests returning to an activity you had previously stopped or paused.
In your context, “get around to it” might be slightly more natural because you’re talking about procrastinating. However, both can work depending on the nuance you want.
For example:
• “By the time I get around to it, it’s already 11 PM.” (Natural and fits well.)
• “By the time I get back to it, it’s already 11 PM.” (Also works, but it suggests you had been working on it earlier and paused.)