Perhaps use the raster
package, this won't work for all NetCDF files but it does for yours:
library(raster)
## brick reads all 22280 layers
r <- brick("obs.nc", varname = "tasmin")
## extract works for all time steps
vals <- extract(r, matrix(c(-120, 52.5), ncol = 2))
dim(vals)
## [1] 1 22280
Note that gives a 1-row, many column matrix because I only gave a single point to extract()
.
(The extraction is simple with direct copy from the nearest cell, use method = "bilinear" to do interpolation). See ?extract
for other options.