Not true, prop falls sharply at 24h (+/- 6h). For some people (eg. Vince Carter) this can be a dramatic noticeable fall in levels, within a day. With daily injections of prop, everyone experiences a dip before injection (look at the prop graph, superimposing several daily injections creates twice the levels at 12h post injection compared to 24h post injection)
I've been saying it that even with daily shots you have a peak, and then a trough. Stable is misunderstood as some sort of constant level and that's a mistake. Less variance in the peak and trough is as good as it can get.