The pivot is grammatical, not thematic
In Japanese, the pivot works because the same clause can be read with the line above or the line below — usually because a particle or a verb ending has two possible attachments. Line 3 finishes the five-seven-five and also starts the seven-seven. English has to fake it, and the usual fake is a line that reads as an ending and as the beginning of a new clause.
In the specimen, the empty room closes the light description and also opens the keys clause. Both readings are grammatical and both are true at once. If only one reading works, there is no pivot, and the poem becomes a five-line statement — which is a different, weaker form.
What the two extra lines buy you
Haiku ends on a gap. Tanka ends on a person. The seven-seven tail is where the speaker appears, usually at a slight angle: still holding, still waiting, still not saying. The two lines are long enough for a whole clause of human behaviour, which the three-line form cannot hold.
Drafting order that works: write lines 1 to 3 as a complete haiku with no speaker in it. Then write lines 4 and 5 as the thing the speaker was doing while the first three lines were happening. If lines 4 and 5 explain the first three, cut them and start again.
Counting and the modern free tanka
Counting on in English is even more approximate than in haiku, because five lines give the approximation more room to drift. The specimen counts 5 / 7 / 5 / 7 / 7 in syllables. Short lines are safer than long ones: an English line of eight syllables next to a seven reads as long, whereas six next to seven reads as short.
Since the 1890s, Japanese tanka has mostly been written free of the on count. You can do the same in English, but then keep the pivot, because the pivot is the form. A five-line free poem with no pivot and no turn is a short lyric, not a tanka.