the triangle in the box looks more like a delta, time unit type thingy, whilst the triangle alone just looks like a triangle and nothing more, and is alittle confusing as it looks like your other triangle which i've forotton the meaning of...
Anyway, the triangle alone is prettier, but makes me think "gate" rather than "time delay", ergo I'd go for the boxed one, or preferably a prettified version of the box one, maybe in a sharpened box?

but then in most things I go for function over appearance, though both is best...

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