SQL group by help

I'm trying to create a visual representation of a 6x8 grid of samples on a
rack using the following SQL format:

with rack_display as (
select sr.ts rack_ts
, sr.rack_id
, r.rack_barcode
, 1 as row_pos
, max(case when rack_well = 0 then 'A1: '||sample_barcode end) as
col1
, max(case when rack_well = 1 then 'A2: '||sample_barcode end) as
col2
, max(case when rack_well = 2 then 'A3: '||sample_barcode end) as
col3
, max(case when rack_well = 3 then 'A4: '||sample_barcode end) as
col4
, max(case when rack_well = 4 then 'A5: '||sample_barcode end) as
col5
, max(case when rack_well = 5 then 'A6: '||sample_barcode end) as
col6
from rack r
, sample_rack sr
, sample s
where r.rack_id = sr.rack_id
and sr.sample_id = s.sample_id
and sr.rack_well < 6
group by sr.ts, sr.rack_id, r.rack_barcode, row_pos
union all
select sr.ts rack_ts
, sr.rack_id
, r.rack_barcode
, 2 as row_pos
, max(case when rack_well = 6 then 'B1: '||sample_barcode end) as
col1
, max(case when rack_well = 7 then 'B2: '||sample_barcode end) as
col2
, max(case when rack_well = 8 then 'B3: '||sample_barcode end) as
col3
, max(case when rack_well = 9 then 'B4: '||sample_barcode end) as
col4
, max(case when rack_well = 10 then 'B5: '||sample_barcode end) as
col5
, max(case when rack_well = 11 then 'B6: '||sample_barcode end) as
col6
from rack r
, sample_rack sr
, sample s
where r.rack_id = sr.rack_id
and sr.sample_id = s.sample_id
and sr.rack_well >= 6
and sr.rack_well < 12
group by sr.ts, sr.rack_id, r.rack_barcode, row_pos
union all
...
)
select * from rack_display order by rack_ts, rack_id, row_pos;

the "union all"s continue for another 6 blocks. reports would filter on
rack_id and timestamp.

if timestamps for each load of a rack were guaranteed to be the same, this
would work. however, the "sr.ts" values may vary by a few seconds so there
is potential for the "group by" to break. ts differences will be a minimum
of 5 minutes for each distinct load of a rack.

what i think i need is to manufacture a group by column based off rows in
"sample_rack" that have "ts" values that are < 1 minute from each other and
rack_id is the same. i'm coming up blank on how to accomplish that though.
my first thought was to create an interval of +/- 1 min then find all rows
that overlap and assign a group number but i'm not sure how to accomplish
that.

there's also no guarantee an entire rack is full of samples so some "cells"
of display might be null. i think that makes the use of tablefunc crosstab
a little harder. if i remember correctly, it does not handle missing values
well. i'm open to any pivoting strategy.

anyways, i thought i'd reach out for ideas while i do my own digging.

thanks for any input! let me know if i'm not being clear on the problem and
desired outcome.