Hello, this is Dr Linda, a UK based vet.
I'm sorry to hear Leo is having this issue.
Unfortunately we do know that those cats who have previously had a urinary blockage are more prone to urinary issues going forward.
This is a true emergency is Leo is showing any signs of being currently blocked e.g. straining without urinating, only producing small drops of urine, a tense or bloated abdomen, vocalisation or distress. This would warrant an immediate vet visit.
If Leo is settled and passing good quantities of urine, a visit in the morning should be ok as long as we monitor closely.
This is likely cystitis, which can be triggered by e.g. stress, an indoor lifestyle, a dry diet or being obese.
Other considerations would include an infection or bladder stones, but these are less likely.