https://docs.sentry.io/product/performance/transaction-summary/#self-time

Suspect spans are determined using a span's self time rather than its duration. To calculate a span's self time, take the interval of the span and subtract the intervals of any child spans. The duration of the remaining interval is the span's self time.

It's not very clear how this can be interpreted in a browser context. What is happening with pageload during these intervals?