OC-VCXO Oscillator Spec.

How to understand this spec. of Oscillator?

Accuracy error(Time locked/coasting or start up)
<200ns/1day <10us/1day

<200ns/1day means that the oscillator drifts less than 200ns during one day. Just divide the numbers, that's 2.3e-12 stability. The other words are probably telling you that it achieves such accuracy only when synchronized to some external master clock.

<10us/1day means less than 10us drift per day, or 1.1e-10 stability. That probably occurs when it is "coasting" or "starting up". In other words, not locked to any external master clock.