Start by recording where the hours go for two weeks before changing anything, because the answer is rarely what you assume. Most solo businesses find a substantial share consumed by administration, scheduling, invoicing, and the switching between them rather than by the work customers pay for. Evenings are frequently spent on tasks that could have been batched, and identifying that is more useful than resolving to work less.
The switching is worth attention specifically. Returning to focused work after an interruption takes considerably longer than the interruption itself, which means a day fragmented by messages produces less than a day with two protected blocks, even with identical hours. Checking email at set times rather than continuously is the single change with the largest effect, and it costs nothing.
Then look at what is genuinely creating the volume, because the remedies differ. Too much work at your current price is a pricing problem, and raising it reduces volume while maintaining revenue, which is the outcome you actually want. Work that takes longer than it should is a process problem. Work that only you can do is a documentation problem. Treating all three as a discipline problem is why resolutions to work less rarely survive a busy month.
Set the boundary as a specific commitment rather than a general intention. Not working less but no work after a stated time, and one full day away each week. Vague intentions collapse under any pressure because there is no moment at which they are being broken. A stated time is either honoured or not, and that clarity is what makes it hold.
Tell customers what your hours are and then behave consistently with them. Replying at eleven at night trains people to expect it, and the expectation then becomes a genuine obligation you created. Most customers have no expectation of out of hours response until a business demonstrates one, and almost none will object to a stated working pattern.
Take time off before you need it rather than after. Recovery taken while still functioning is short and effective. Recovery taken after collapse takes considerably longer and usually costs revenue as well. Book it in advance, when the calendar is empty, because that is what makes it survive contact with a busy month.
Watch for the specific belief that causes the most damage, which is measuring your own worth by hours worked. It is common in a first year because hours are the only input you fully control, and it produces a business where working less feels like failing regardless of the results. That belief outlives the circumstances that created it, which is why some owners never recover their time even once the business is comfortable.
And be honest about whether this is a stage or a structure. A demanding period during a launch or a large project is normal and ends. A business whose economics require this pace permanently is telling you something structural, and no amount of discipline resolves it. That distinction is worth making deliberately rather than discovering it two years later.
Notice which work you are actually doing in the evenings, because it is rarely the work that had to be done then. Frequently it is the work you enjoy least, deferred all day and confronted when there is nothing left to defer it behind. If that is the pattern, the fix is scheduling those tasks first rather than working longer, and a business that handles its administration before its client work usually finishes both earlier.