I’d say their quality will deteriorate over time, so the best time to buy them will probably be when the stall opens around 4pm. These dim sum are rather robust, rustic versions of their delicate restaurant counterparts - more additives/flour/etc. than actual meats or shrimps.
They do remind me of old-fashioned dim sum which coolies or blue-collar labourers in Singapore used to have for their breakfasts back in the 60s & 70s - places like Nam Tong in Singapore Chinatown opens at 4am, as these coolies need their sustenance before their work-day starts at 5.30am to 6am.
I’m sure you remember the time in the not-too-distant past when dim sum is a breakfast food - most dim sum spots close down by 10-11am, unlike today where people have it for lunch. In London Chinatown, they even serve dim sum for dinner!
