Coordinate Structure: “一会儿……，一会儿……”
In Chinese the pattern “一会儿……，一会儿……” (yíhuìr..., yíhuìr...) shows actions following one another in quick succession, or two states alternating.
Basic Structure
一会儿 + state / action 1，一会儿 + state / action 2
In English:
One moment …, the next …
or
Now …, now …
Examples
它一会儿在你脚边睡觉，一会儿在你身上爬。
One moment it's asleep by your feet, the next it's climbing all over you.
Structure
一会儿在你脚边睡觉 + 一会儿在你身上爬
sleeping by your feet + climbing over you
它 — it
一会儿在你脚边睡觉 — one moment it's asleep by your feet
一会儿在你身上爬 — the next it's climbing on you
Here two different actions alternate.
他一会儿进来，一会儿出去，忙得很。
He keeps coming in and going out — he's very busy.
Structure
一会儿进来 + 一会儿出去
comes in + goes out
他 — he
一会儿进来 — one moment he comes in
一会儿出去 — the next he goes out
忙得很 — is very busy
In this sentence 进来 and 出去 follow one another in quick succession.
最近天气变化很快，一会儿冷，一会儿热。
The weather has been changing fast lately — cold one moment, hot the next.
Structure
一会儿冷 + 一会儿热
cold one moment + hot the next
最近 — lately
天气变化很快 — the weather changes fast
一会儿冷 — cold one moment
一会儿热 — hot the next
Here two states — cold and hot — alternate.
Quick Rule
一会儿 + A，一会儿 + B
Meaning: two actions or states alternate within a short space of time.
Examples:
一会儿进来，一会儿出去
in one moment, out the next
一会儿冷，一会儿热
cold one moment, hot the next