一度 vs 一时 (at one time vs for the moment)

Once, for a while

• Your uncle talks about a difficult period in his life and a moment of panic.
• his他tāat one time一度yí dùunemployment失业shī yè，then那时nà shíhis他tāfor the moment一时yì shínot不bùto know知道zhī dàoshould该gāiwhat's to be done怎么办zěn me bàn。 — "He was unemployed for a time, and at that moment he didn't know what to do."

at one time一度yí dù = at one time, for a period (in the past)

• at one time一度yí dù + verb / adj = once, for a while in the past (and it is no longer so): at one time一度yí dùdegree / adjective linker很hěnpopular流行liú xíng, at one time一度yí dùto cut short中断zhōng duàn.
• It describes a past phase.

this这zhè(measure word)首shǒusong歌gēat one time一度yí dùvery非常fēi chángpopular流行liú xíng。

for the moment一时yì shí = for the moment, temporarily

• for the moment一时yì shí + verb = at that moment, for a short time: for the moment一时yì shícan't recall想不起来xiǎng bu qǐ lái (can't remember just now), for the moment一时yì shíto have an urge冲动chōng dòng (a moment's impulse).
• It is about a brief moment, often a temporary failure.

his他tā的dename名字míng ziI我wǒfor the moment一时yì shícan't recall想不起来xiǎng bu qǐ lái。

A phase versus a moment

for the moment一时yì shí in set phrases

• a short time一时半会儿yī shí bàn huì er = in a short while: this这个zhè gequestion问题wèn tía short time一时半会儿yī shí bàn huì er解决不了jiě jué bù liǎo.
• at one time一度yí dù can also be a count: once a year一年yì niánat one time一度yí dù — "once a year": once a year一年yì niánat one time一度yí dù(modifier / structural particle)的deSpring Festival春节Chūn jié.

once a year一年yì nián(once)一度yí dù的deSpring Festival春节Chūn jié。

Recap

Read the full reference: HSK 6 grammar — Comparing similar adverbs.