The bare noun is זְמַן, time. But the root's deeper sense is to fix a time for something, to appoint a moment, and that is where the family gets interesting. To invite or to order is לְהַזְמִין, literally to set a time for someone or something; an invitation, הַזְמָנָה, is the same act named. When something is ready and set for its moment it is זָמִין (available), and a chance that presents itself at the right moment is an הִזְדַּמְּנוּת, an opportunity. Even cash, מְזֻמָּן, is money "made ready" on the spot. One root: time, and everything that is set in time. Every word here is verified against pealim, niqqud included.
The same root runs through the verb system. Each binyan is a voice: it bends the one idea into active, passive, causative or reciprocal. Tap to hear.
The everyday verb is the hif'il לְהַזְמִין: to set a time for someone (invite) or for something (order). The pi'el לְזַמֵּן (to summon, to convene) is more formal. The reflexive hitpa'el לְהִזְדַּמֵּן (to come up, to happen by chance, where the ת becomes ד before ז) gives the opportunity noun below.
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.