How do I ask for a date in online dating?

Online dating is all well and good, but ultimately online is just a means to an end, namely to date online. How and when do I transition from one to another?
There is no general rule, since a lot of it depends on the platform (at a flirt app you tend to arrange a meeting quicker than on a matchmaking site), much of it depends on the partner (younger singles arrange a meeting sooner, single mothers who aren’t in quite the same hurry as college students, who are new in the city and are looking to meet people anyways) and sometimes a first date will succumb to circumstances (if both parties live in different cities or have to work a lot and have little free time).
Regardless of how long it takes to agree on a first date – you should definitely not wait too long to bring up the subject. Once it’s clear after a few messages that you like each other, you should ask for a date. Best mention it casually in a message with other topics and if possible with a concrete plan and options for an alternative. Then your counterpart makes their play, at least the intention is clear: “I want to get to know you – not just online”.